Yep, not a lot that can be done to get more engine power. Weird, huh? But damn near everything has been tried in the last 17 years and nothing has ever really amounted to much.
However, suspension upgrades are readily available and have a profound effect. I'd definitely start there; you can make the Vee handle a LOT better.
And as mentioned, changing gearing is pretty common, fairly easy and cheap, and will give you more poke out of corners.
But the best money you'll ever spend is on upgrading your own software. Take a class or two on rapid transit via motorcycle; I can highly recommend Total Control Riding from Lee Parks. Speed is 90% rider, 10% bike. It's not engine power that's holding you back.
The only positive performance effect an aftermarket exhaust might have is that it's lighter. The stock cans are pretty heavy.
However, lighter cans will also be MUCH LOUDER. It's up to you whether you can tolerate the splitting headache from two pounding pipes mounted up high near your head. A four-cylinder bike with one pipe and an outlet further away is much more tolerable. A loud Vee can be seriously unpleasant.
2002 Suzuki DL1000 V-Strom, Dark Metallic Space Blue
1983 Suzuki GS850G, Cosmic Blue
2005 KLR685, Aztec Red - Turd II.2, the ReReTurdening