Names and registries are a minefield, aren't they? No matter what you try, it seems like you're going to conflict with
something...
I agree completely that the "Enterprise" refit was a bad idea due to the length of time it took--actually, my feeling is that the length of service enjoyed by the Miranda and Excelsior can actually be somewhat explained away by this. Perhaps, after the experience with the Connies, Starfleet resolved to never have ships out of action that long again, and designed the Mirandas and Excelsiors in a more modular fashion for easier upgrades. All that said, the "Enterprise" refit seems to have been the way Starfleet went, since every other Constitution we've seen post-TMP (which admittedly is only about two: the Ent-A/"Yorktown" and whichever one got toasted at Wolf 359) had that refit. Thus, Stress and I have envisioned the Phase II only as the prototype to the TMP refit, and in fact as something of a failure. (If you're interested, you can see my full writeup on the Phase 2 at
http://www.trekmods.com/scripts/ship_description.php?id=75&mod=iaw.)
It's also possible, I suppose, that the length of Enterprise's refit was influenced by the fact that it was the first time it had been done--other refits might have gone faster once the procedures had all been worked out...