Winter Garden huh? Winter Park here.
Welcome to the LOC.
I'm not sure what your refering to about the suspension being more of a drop in the rear than the front. Do you mean why do people have or like that set up??? What is it that you would like to do with a new suspension? Do you want to lower it, or replace the stock suspension and maintain stock specs?
As for the CAI. The SRT comes with a piggy back chip that you solder in to the ECU. As far as I am aware they are the only ones. the rest of them are only intake systems. As for going generic, that may or may not be a head ache you may not want to deal with. I would use a name with a proven background. K&N, Injen, SRT, and a few others. Some people say that the cold air intakes don't do anything for the IS300's though. SO you might wanna wait till you find out more before you go out and get one. I have a brand new K&N Typhoon in the garage I was going to put on, but I have decided to go supercharged, so I was going to sell it. If later you decide you still want to go with a CAI, let me know if your interested. I'll sell ya mine.
But to answer your question, they all perform about the same. I think it's more about fit and quality. K&N is the only one I know have that comes with a Dyno sheet to show performance. I guess that made it worth more to me.