Although discussed many times over, I'm not a "use the search" nazi, so here's the low-down:
1. Shock towers. Replace them immediatly. And don't go with cheap-o aluminum ones on e-bay - go for the dynamite, or Storm Pro, or Hardcore Racing shock towers. The hardcore racing ones own but they are very expensive ($42 each); the dynamite ones are the same metal as the Storm Pro ones, and they are red. Fioroni makes some too, but I'd rather just have the Hardcore Racing titanium ones over them (Fioroni is usually not cheap.)
2. Pipe. Ditch the GS noisemaker and get another pipe - any pipe really. You're better off going with a low end pipe. A decen't pipe isn't too expensive. There's no performance advantage to an "in line" pipe but they are more durable (and more expensive usually.) The stock GS engine is a good runner, and it will do a lot better with a good pipe. This isn't really a durability thing but it's the first thing I did to mine.
3. Hinge pin mounts. These are hard to find right now and kind of expensive. This will replace your plastic ones. Dynamite makes them, for about $12 a pair, but I have not seen them in stock anywhere for months. Horizon is out of the GS Storm Pro ones too; but the GS ones are expensive. You can find them on e-bay a lot but expect to pay for them. For the time being, you can put longer screws in your plastic ones, and put a lock nut on top to hold them in place. This works well for some people. The whole problem with the plastic ones is that the screws like to back out, and when they do, the whole arm can swing and snap, possibly damaging the shock, dogbones, etc. Check the screws often.
4. Consider getting a hexscrews (hexscrews.com) set. These are about $30 and worth it. It will convert your storm to all hex screws, and they are very tough. And the good thing is that you will have all your old screws as backups when you bend one (it happens..) Note that the Hexscrews set for the Storm RTR includes longer screws for the plastic chassis braces. Forget the RC Screwz set, I got this one and although the silver screws look nice, I've stripped out too many of them to ever consider getting them again. They also tend to bend pretty easily.
5. If you haven't already, make sure you ditch the 4-cell pack and get a 5-cell hump pack. Much more powerful. While you're at it, try to get a better steering servo, and move your JR 590 to the throttle position for better brakes.
Really, the shocks towers are important. You'll bend the RTR ones immediately. Beyond this, the benefits will be smaller but each one helps. Things like the carbon fiber plates are nice, especially the center diff one with the bearings for the brakes. The two-peice center diff holder from Dynamite is also nice; it's more rigid and makes pulling the center diff a lot easier.
A quick hopup you can do is to replace the bushings in the steering arms with bearings. This will help smooth the steering. The Storm Pro steering plate is very nice too.
If you plan on getting CV driveshafts for the thing, which you can often get at resonable prices on e-bay, keep in mind that the center CVD's will be too long for the Storm RTR chassis; you'll have to upgrade to the Storm Pro chassis at the same time. (You can often find the Storm Pro chassis on e-bay for a resonable price.) The Storm RTR center dogbones will be too short for the Storm Pro chassis, so if you upgrade either you have to do both at the same time.
Some people have had issues with the chassis braces (torq rods they are sometimes called) popping out of their ball-ends. I never had the problem, but I did upgrade to the Storm Pro chassis braces anyways. They are more rigid. Another problem some folks have had that I don't is the bulkheads snapping where the shock towers attach to them. Fioroni makes a rear bulkhead brace that will solve the problem, but I have not felt the need to get it because I never had one break. Bulkheads are cheap anyways =)
One thing I suggest you do is mount the wing mount differently to the bulkhead/shock tower. There's four screws holding it in place. I use longer screws on the bottom, and then screw them right through the bulkhead and throw a locknut on the other side. Since I did this I have not had my wing mount rip out of the bulkhead; it happened to me three times before I did that. It didn't really break anything, it would just strip out the bulkhead's screw hole and the wing would fall off.
Last but not least, make sure none of the plastic parts are binding with each other. I had to pull apart my front end when I first got the thing because everything was so tight. I just used some sandpaper and opened up a few places just a little bit, like where the C-Hubs sit and the upper suspension arms hook up in the middle. Once I went through it, it was really nice and smooth.
There's a lot of cool hopups for the Storm out there, so have some fun with it =)