...Do the strut tower bars even do anything?
yep mine sure has
I've had APR, RMM and now Carbing
APR would be the best value of the 3 .. and does it's job quite nice as there are no welds that would cause possible flex as you want the stiffest bar.
There's more stability with the strut tower bar on as compared to nothing being there when you do hard cornering is when you feel the celica holding down better..
If you do a lot of fast turns that's when it's felt
Though i've read with sway bars you feel the most difference and i'll have to get some of those in the future..