Yes, I don't think I'll mess with the registry. I think these problems arose because I rolled back to a restore point before I reinstalled Excel 2007 to compare with Office 365 Excel.
The restore said it had worked successfully, but clearly it did not, as Office 2007 remnants are still on the system. It has also left me with Pending Windows Updates that the history says have been successfully installed.
Never had a problem with restore points before, but I'll be very wary about ever using them again - clearly not error proof.