For you guys arguing over whether or not ballast is beneficial, well to put it simply it is beneficial. Not only is it good for different weather conditions but it does massively improve cornering in some cars for some specific tracks. These variables are what is important, because for every car, you truthfully should have a different tuning set up for each track. Shame GT5 doesn't allow us to have load outs for each track. Some tracks ballast would probably hurt you, but other ones it can be an immense help. As for it being a substitute for heel toe braking, I'm not so sure about that. In real life heel toe is obviously necessary, watch any of the time attack drivers' replays on youtube or streetfire and you'll see that.
However in my experience within this game I don't see it as playing a huge role. I personally have tried different set ups and find the analog stick gas/brake to be the best for pure throttle and brake control. If you've mastered it, and depending on whether or not you use ABS, you can have more control over your handling than using heel toe braking. You can move the thumbstick much faster than someone in real life could switch between the gas and the brake, so this method really does allow you to have ultimate control. By slamming the brake initially going into a turn, then letting off the brake slightly, while altering throttle control at low RPMs through the turn, your lap times will seriously improve. Setting up the e-brake in a good position (R2 when using R1/L1 for shifting) also helps handling when using the thumbstick for throttle, as this allows your turns to become even more precise. Give it a try for a little while before you dismiss it, if you can get good at it you'll be greatly rewarded.
I do recommend getting some kind of thumbstick cover like someone above me mentioned though. Having a silicone cover like the dominator grips really enhances your control even more. As for the trigger upgrades, I have them and they're useful if you use these buttons often, especially for FPS games, however in GT5 I don't use these buttons that much so they aren't as beneficial.