Actually there are a lot of upgrades when it comes to the J75.
"The only upgrade they offer is inline spectrophotometer, which just speeds up calibration. " I really think calibration is something which should be done daily. It has been automated it is easy to do, causes less errors and safes time. The inline spectrophotometer is viable piece of extra equipemtent. U can also automatically do output profiles with it.
J75/C75 also have inboard outboard density reading software. This has nothing to do with the RIP, but it actually changes the power of the lasers when it comes to inboard outboard density controll.
The Fuser has been changed also. It now has settings for different papersizes.
Feeders have some slight changes also and now the operator can change the rollers in few seconds.
There is a new SIQA tool which really helps u to get that registration spot on.
I think u should go and see all the new features on the new c75/J75.
When considering the J75/C75 i would really go and demo the machine. I was impressed by it when it comes to light production.