So the primary problem is the tank swelling, if it hasn't it will, if it has it may not get much more out of shape. There isn't an answer to this other than a new tank which you won't be able to find or replacement with a custom metal tank.
The clutch, if it's OK will probably remain OK. Don't start worrying about it.
The brakes are adequate, just don't use any sintered pads, go for soft organics. I am using Brenta pads on mine cheap enough to replace regularly and they work fine. The rear is a perenial pain, though it was on all of the 750's I had, they trap air and get a bit useless. Saying they are weak is when you compare them to something else, usually a higher spec system which is a bit like me complaining that my Duster isn't as quick as next door Audi.
The suspension, rear certainly will be getting a bit tired but if you change that the front will show it's flaws (no adjustment of anything). You can get full internal replacements which make the front much better (adreani misano units) OK it's a transformation but then the back shows itself up as not brilliant so you either live with it or change it too so you can spend about 1K on the suspension. BUT the base set up is good enough as is. No where near as good as say my 748R's but then that has race grade suspension so it isn't going to be!!
The exhaust system will probably be non-standard, ditching the 'udder' is possibly the most common change you'll find and after-market silencers are often found. Mine has Termis and are quite nice tucked onto the end of a de-uddered system.
And of course the controvesial tail chop, mine has been and I think it makes the bike look massively shorter and even more 'insecty' I know an odd description but it works in my head (it is a very strange place LOL)
If the bike is clean and tidy then it'll be a good bet. Without doing too much, belts are the main thing, it will work and it will be fine. Don't sweat about the valves as unless there's lots of wear they won't change too much, worth having checked though.
If you don't like something about it then change it, it is very difficult to find a totally standard old style monster, something has always been done to them.
Things done to S2R's ...
The most common is to loose the udder, google it or look at original pictures
Upgrade to goldlines or even radials, not uncommon but a pain as you needed different discs through to fork legs for radials. I have some spare goldlines but haven't bothered, but they'll look very nice when I do if I do.
If you plan to go out in the dark the original light unit is not the best, I have a completely LED based replacement unit... BUT you'll need a mount ring as most lights units or reflecters are smaller so won't fit
Luckily Mr Gazza hopefully still has a few rings he made which are great.