Aloha d,
Up-dated/graded from:
Lion (10.7.x) to Mountain Lion (10.8.x) to Mavericks(10.9.x) and never had a hitch.
You should have no probs going directly for 10.7 to 10.9.
Couple of things to just make sure:
1-Your machine can make the change. (My laptop is stuck at 10.7.x because it can’t go any higher)
2-Do general maintenance stuff. Permissions/de-frag/clean caches etc. The free app Onyx is good for this.
3-Back-up Back-up Back-up Back-up Back-up just in case.
Good Luck!
{‘-’}
Tip:
Once you do update to Mavs, (and before running Cubase) use it for a while (a few days if possible)
because it is quite diff from Lion. Many new changes afoot.