Concerning old bikes, ther´s no difference in parts.
It´s not easy to get an alternator for a jap. brand or an old beemer...just same complicated...buuut almost every shag can repair them. Suspension is no difference between old bikes and new bikes.
I ride a R100GS from 89, very modified and very easy to repair.
Even a torn valve which caused a total brakdown was repaired in south of spain within a week.
So I would look for an old bike which is easy to repair, avoid fuel pumps as they tend to break with fine dust you find almost everywhere and you can´t avoid it.
they key to succes is that you know your bike and you know how to repair and maintain it. It´s not the question of brand, it´s a question of your knowledge an what suits you. I would never change my ride, it took me everywhere I wanted to go (last time to Japan).
BTW. one maintainance per year:

__________________
KurvenfiebersReisen.blogspot.de

Well things like the z650 were a pile then and even worse now, Japanese build quality back then wasn't good and kwacker were also furthest from the grease pot out of the big four when it came to initial assembly. The brakes, forks, suspension etc are terrible when compared to even a modern budget bike..... Rose tinted glasses comes to mind and as u say they are not cheap. Who in their right mind would pay six k for a fizzy? Well my mate for a start, also paid big money for a Z900 and an Xjr 600, that's why I know they are piles.
I'm sure there will be tons of people who did a million miles on a cx500 and won't like what I'm saying........ They are not the ones who will have to ride what ever u buy everyday for how ever long u take. Stick to a modern low tech bike that has a good spares back up and is common to where u r going......... Prob a Honda.

Are you honestly saying that suspension technology has not changed in the past 30-40 years?

Do keep in mind Herr Kurvenmeister is riding a nearly 30 year old BMW GS Air head ... which, in my experience, was not the most RELIABLE bike ever produced.

... my best friend owned a '92 for 20 years and I rode with MANY R100GS's in the 90's all over USA, Mexico. So many problems ... mostly electrical. I towed a few and also owned an R80GS and a very troublesome R100RS myself.
Both disasters.

Such a poor charging system design. BMW (back then) could not even design a proper throttle mechanism. Even Harley got that right.

But there are many die-hard BMW Air Head fans out there and the smart ones have done the MANY mods required to keep those old nails running ... and for those who travel ... they carry required spares on board. When all is set up correctly ... they are capable motorcycles! (for a 1980's design! :smarts
Look at Grant, owner of HU. He is an expert Air Head BMW guy having spent years going RTW on his Air Head. These days,
knowledge and experience is what it takes to keep the old bikes running smooth.

But some suffer from dreaded "Teutonic Myopia" where it turns out they have very little experience on other brands of bikes ... and especially avoid Japanese machines.
We have several Air Head GS riders in my riding club ... even a nice original R80GS ... which BMW and others claim is the "First Adventure Bike"! (I guess they weren't around in the 60's and 70's when me and my buddies toured around Baja on our Honda 175's, 250 Scramblers and XL250's.)

But to travel on an older bike may be a challenge in another way. In USA at least many shops will NOT work on older bikes. This true for some BMW shops and multi line dealers as well. They just don't want to be responsible for all that could go wrong on an unknown machine 25 to 30 years old.

But here in San Francisco Bay Area we have specialist shops who service older bikes ... both
BMW and Japanese bikes.

In much of the 3rd world the mechanics can figure out just about anything .... and they probably are THE BEST for working on older machines. They will fix it ... one way or another!

Apples to oranges. So newer bikes are harder to work on and older bikes are easier to work on? That's almost completely contingent upon the bike itself. I've worked on modern bikes and older bikes. I built my motorcycle from the ground up that I rode on my trip. It was a 2007. Not very difficult at all. I do know that my clutch went in Guatemala. Went to the shop on Monday, I was in Xela and a new clutch came from Guate City, and by Wednesday my bike was up and running. So you're telling me that if I had a 90s bike the repair would have been easier or faster?

Hogwash.

Now, for me, I would buy a travel bike that has EFI and ABS (not as critical to me) and that's it. No traction control no electronic throttle, no electronic cruise control or suspension. The new bikes that have come out in the past 7-8 years seem to be inundated with electronic "goodies" which, to me, only present weak points that could be unrepairable in the field.

Still, I'm not buying that an 80s-90s bike is a better option for round the world travel. It's doable, people ride the world on scooters, posties, GSXR1000 sportbikes, and everything in-between. I just don't see the point in swimming against the tide.

Cholo, not only has my friend owned these bikes I am of an age to have owned and ridden them when they were in their prime.... The list would include all the various Lc yamahas, H1 and H2 kwackers, a z1000j like u, Gpz1100b1,, GS 1000, 750 and 550 et s, laverda jota etc etc etc plus dome of the smaller strokes when I was on L plates. They are not the tech masterpieces you make them out to be, good in their day but now suffering from years of abuse, poor repairs and poor materials. I even despatched some of these around the UK in between jobs. If u honestly think that an 80s Japanese bike is comparable to something available now then I think u need to take off your glasses fella. Failing that I can sell u an 80s Z900 for 11000 pounds!!!
Ur be telling me next the Z650C was the pinicle of Japan engineering and reliability

Btw thank you for the compliment , biggest load of rubbish is not bad going considering what gets posted on this site if u like we can argue about the fantastic engineering in capri s, granadas and Cameros , I've owned lots of them too

No offense taken......... Though the phrase with all due respect is usually a pre cursor to something else.
That said my ding a ling is bugger then yours

Back to the point, ride what you like, because even if you do have a problem it won't seem like one just a challenge or hiccup on your trip. And when you get back and you look back, it won't be the 10000km you did and only needed to stop for fuel you will remember, but the week you spent waiting for parts/repairs when you had a fabulous time with the locals!
Joe

I honestly said "heavily modified".
That includes the suspension.
Rear shock is an air shock from Fournales, no spring, just oil an airpressure, the front fork is modified with Marzocchi Cartouches.
So yes I can honestly say, that suspensions have changed a lot in the past years. The fournales was just suited for Jets, now they´re adapted for all kinds of vehicles...

__________________
KurvenfiebersReisen.blogspot.de

I regularly ride an 81R80GS, 1986R65 and a 95 R1100GS in very remote parts of Alaska, Yukon and Northwest Territories every year ... with no major issues ... just routine cyclical/custoidial maintenance. However the 71 Triump Daytona that i bought new in 1972 was/is a maintenance nightmare with major breakdowns from the very beginning on every longer trip i took. I still ride it locally in the Oregon Great Basin Desert when winter really sets in Alaska ... just not very far from help. I'll probably turn it into a garden ornament at some point.

Now the real problem is being an old motorcyclist I have many more breakdowns now than i used to remember ... when i can remember. But i still ride anyway. Ride what ya got ... old or new ... now ... sleep next winter (8->}

__________________
There is no path. You make the path as you ride.