I did a super thorough uninstall of both 7.06 and 7.5, reinstalled 7.5 - and now it works!
Cubase 7.5 has been super stable for me. I just recently upgraded to Mac OS 10.8.5 (I’ve kept it safe for a long time with 10.6.8). Btw, I’m not implying that the issue at hand has anything to do with the operating system - I would not know.
Before I reinstalled I could see the folder where the track presets should go. I could even have old (7.0.6) track presets there and they would load with no problems. But still no saving of instrument tracks.
But anyway, a fresh install did Cubase good. I you wanna try, this guide worked for me: