I bought my ST1100 new in 2001 and have been all over North America and Europe with it. The bike has about 180,000 km on it now. Later this week, I'm going to get on it (in Zurich) and ride up to the Baltic countries, St. Petersburg, and Finland.
I'm very happy with the ST1100. It is heavy, that is its one and only disadvantage - but, like any motorcycle, that issue disappears once it starts moving. It can cope with gravel roads, if you happen to get stuck on one by accident, but I wouldn't call it a pleasant experience. If I have to do 5 miles on a gravel road to get to an interesting place, fine, that's no problem, but any more distance than that is a stressful nuisance.
To me, the great strengths of the ST1100 are:
- legendary reliability (I've never had a breakdown of any kind)
- all the power you would ever need - even on the autobahn
- excellent weather protection (I've ridden thousands of miles in below-freezing weather, and rain is a non-issue)
- enough storage space in the 2 panniers for a month-long tour
- the ability to 'transit' 1,000 km on motorways one day, then throw the bike into the twisties in the small alpine passes the next day.
I don't do my own maintenance, although I would feel confident doing about 90% of the scheduled maintenance myself if I had to. I drop it off at a Honda dealer in Switzerland each fall for what I call 'major preventative maintenance'. That costs about $1,000 a year (the Swiss aren't cheap, but they are good at what they do).
I get about 7,000 km out of a set of tires. When I get the tires changed, I also get the oil and filter changed, and most of the time, the front brake pads changed. The front brakes could easily last 10,000 km, but it's too much of a PITA for me to get them changed (while travelling) between tire changes.
There is a very active owner community on the internet, and all the 'issues' with the model have long since been identified and solved. You won't have any surprises with this bike, that's for sure.
I would quite happily buy a ST1100 again. I can't help you with a comparison against a ST1300 - I don't know enough about that bike to comment with authority.
If your main interest is long distance touring (i.e. riding more than 1,000 km a week when you are on holidays), then for sure, a ST1100 would be the perfect bike for that purpose.