I think it is very nice, but like partial said above, tedious.
Ive tried a few times, like making a "VCV" bank for popular UTAU like Acme Iku, Hakaine Maiko, etc. The results are nice, but I dropped it halfway cause of how much work it needs ;A;
EDIT: However if you can record the VCV bank yourself, I'd say it is 100 times better cause it is natural transition between phonems.