Hi, generally sound bikes, check for usual corrosion areas, like Af Twins check splines on the gearbox output shaft are ok (Not heard of many probs on 650 Alp).
Fuel consumption as standard is relatively poor at 47mpg, seemingly regardless of use which gives 200 miles to running out.
Chopping the cat/subchamber off gives much improved throttle response below 5000rpm and a slight improvement in economy.
After much experimenting, drilling a few holes in the airbox lid improves economy to an easily achievable 56 to 58mpg, giving a total range of around 240 miles to empty. This is with stock carb jetting.
Two important points tho, depending on your intended use for the bike, access for DIY maintenance is quite poor compared to the earlier 600Alps and first gear is also higher on the 650's which may not be so good for rougher stuff.
The 650 makes a better road bike due to a bit more grunt and tighter handling due to firmer suspension - also copes with luggage / pillion better.
By the way I've had two 600 Alps and now run an '02 plate 650 and loved 'em all!