Obviously, Robert Abel has passed on but most/all of the main players are still alive with regard to the early work on TMP's effects. Ed Verreaux
http://www.imdb.com/name/nm0894835/) was one of the guys who worked at Abel during the time they were working on TMP. Andy Probert might be willing to divulge some information. He's a nice guy, but I found it difficult to pin him down long enough to get a detailed coherent account of his recollections of those days. Maybe someone else would have better luck. He's been interviewed a lot, but not so much about this specific period -- mostly the period after the transition to Trumbull and Apogee (John Dykstra's old company). John Hughes of Rhythym and Hues is another person who came out of Abel (not sure the extent -- if any -- of his work on ST:TMP)...BTW, Con Pederson was working there at last check (Scooby Doo 2: Monsters Unleashed)...
Illustrator David Negron, Sr. might make for an interesting interview as I believe he did many of the pre-production paintings that are out on the Forgotten Trek site.
You're right about some people being unwilling to talk about it. As I pointed out earlier, Pederson is one of those people...for whatever reason. I respect his privacy, but if anyone could get him to open up on it that would be a MAJOR coup, in my opinion. Now that Abel has passed away, Pederson is the person with the most seniority that worked on ST:TMP of the Abel team. He was the visual effects supervisor.
Of course, now we are going to be fighting time/memory. How much can one truly remember from a job that took place thirty years ago?
One of the things I ran into when interviewing Taylor and Andy Probert was that there was this difference of opinion of who actually did what...and stories sometimes not aligning. I don't think this was malicious in any sort of way...I think it's attributable to so much time having passed and people's memories getting fuzzy.
I've always been more interested in the Abel team story than that of Trumbull and Dykstra...only because I think that was covered so well in Cinefex and other sources. I'm not sure there's much to add to the "official story".