lol - if you want insurance companies to consider you, your best to forget about making mods to the car :)
Seriously tho, you could try a k&n filter, and perhaps some sort of a cold air intake - this shouldn't cause grief with insurance and will yield some very small gains.
Most mechanical stuff is going to hard with insurance. Honestly, I'd pretty much live with it until your older (better insurance) and can get something better. Short of dropping in a 4agze(?) ( the s/c donk anyways ), I doubt your going to make any changes that are incredibly startling. I'd throw on a cheap set of alloys and be happy with a car that looks a bit better than std, even if it doesn't go much better...
About the best thing you can probably do apart from the filter, is to ensure that the car is running as best it can. I.e. make sure it has decent, correctly adjusted plugs, decent leads, has had filters (oil / fuel) changed within living memory etc. I guess what I'm saying is ensure its maintained in tip-top condition, so that it can give you its best... And perhaps see if you can feel any difference with optimax/ synergy.
Otherwise, check out one of the corolla forums / sites ( a few other there ).