Most of the so-called mods out there do very little to really improve your car. In fact like one of the member signatures, many perform WORSE than stock. Unless you go all out and do some engine swap and/or turbo it. Then it will be a hassle, and no longer a joy.
The tc on its own is pretty fast. Now by fast I mean it's fast in its class. It's actually 1 second slower than the IS300 to 60mph I think. But I think it's fast enough and not too fast to get me in trouble.
I think tunners like to add HP and do all that, but unless you are a dedicated tunner and enjoying doing all these stuffs, the time, money (400 to 600 for a pipe, hahaha) wasted is not worth it. I rather buy a few more CDs, rip them and put them in my Iriver MP3 player and enjoy them as I drive
Unless Toyota offers a supercharger, otherwise I won't even bother with little things.