Nothing, zero, runs better than new.
Only items I've had to work on were normal maintenance (i.e. oil, tires, forks, carbs, brakes, lube, etc.). I've enjoyed working on the bike and getting to know its ins and outs.
Carb cleaning, tuning, and synching are very important to keep the bike running 100%. (Synching is not hard, and must be done if you want to feel how your bike is supposed to run).
Replaced my front brake lines with braided SS, and the bike now does stop like hitting a brick wall. I would highly recommend this upgrade: cost $110.
Replaced my valve cover and breather gaskets with Real Gasket silicone lifetime gaskets - again highly recommended - easy, cheap, and no more oil seepage at all.
Replaced my vacuum fuel valve with a manual Pingel valve and in-line filter. I personally like this, but can't recommend it unless you need to rebuild your vacuum fuel valve anyway. When I rebuilt my carbs, the bowls had a lot of sediment - that's the reason for the filter.
Replaced the front springs with pre-loaded Progressive. This again is highly recommended. I don't feel that it changes the handling much (other people disagree), but you won't ever have to fool with the air pressure front forks again.
I love it and will never give it up. Suzuki got it right the first time. Excellent combination of balance, handling, power, acceleration. I use mine as a commuter, and ride it every day I can, weather permitting.
The only complaint I have at all is the seat comfort. For me it is not comfortable for more than about 1 hour. My next mod to the bike will be new seat foam and seat cover.
If you can find one of these bikes in good shape, you should buy it - you won't be sorry. It does look dated, but to me that is a benefit since I'm not trying to look like everyone else on the road.
I believe it is the greatest value in riding out there. And when you're not riding, you can polish all that chrome.