Only suspension difference is the early 13 model and even then it is just the tower mounts which can be changed to the newer style if I recall correctly. Issues have mostly been addressed through recall fixes. ST1 has cloth seats, ST2 has partial leather recaros, ST3 has full leather recaros. Also the newer ST2 and ST3 have HID headlights. I believe the 13-15 have standard headlamps on all but ST3 models. The packages also contain different Ford Sync packages if I recall correctly.
I am sure somebody else will chime in with some more details and possible corrections or further elaborations of what I have outlined. Hope this helps!