I have not flown a real 767 but have been impressed with the software you describe. It plainly cannot be anything like the real thing but there are elements that deserve praise from a simulation standpoint. For example, reviewers of the program (admittedly not 767 pilots) said they took a real 767 FMC manual and the one provided on the CD. They report that the same level of technical detail was included in each manual and the simulated FMC could be programmed accordingly. Having spent some time arsing around on FS2000, I think it is one of the best around and works very well for what it is. I would say, "if you like it, use it". It's not like the real thing for sure but do you care.
Hope this helps
Nige