Or any aftermarket struts for that matter for the tC?

I am wondering if you just get the springs how your car feels? Do the TRD struts dramatically help handling or just the ride quality?

I have neither, but I can tell you from previous suspension experience. Getting the trd springs alone will lower the car and reduce body roll and maybe a little stiffer ride. Going with the trd struts and springs will lower the car and decrease body roll even more, ride will be alot sitffer and you will feel bumps more. Getting the rear sway bar will help greatly in performance. The springs are made to go with the stock TC struts so you can get them without the TRD struts. But later on down the rode they will most likely blow out due to being compressed for such a long period of time.