In 1979 and 80, Wes Cooley won the AMA Superbike title with a (highly modified) Suzuki GS1000. Here's a photo of my 79. In 1980 or 81, I put on Russell stainless brake lines. Normal rubber lines should be replaced every five years or so. I also put on Ferodo brake pads, which were the best at the time. I changed the fluid to silicone DOT 5, which was also the best at the time. I've changed the fluid since then, but the pads and lines are the same and work great.
I also put a Telefix fork brace on the spindly 35mm forks, and installed stiffer Progressive Suspension springs. When I got my CBR, I was going to sell the GS, but kept it. I'm glad I did. The Works Performance shocks were $300, but they transformed the bike. It would be creamed on a track, but I can keep up with modern liter bikes on twisty roads. Plus, it only has 54K miles on it. Your front brakes and suspension is a good place to start.