YES! Do it! ;D
HD mod was into my head too
I was thinking the same, with some edits of KOF XIII sprites.
I started making some edits, but stopped seeing the amount of sprite editing work. Can you imagine a mod with Kof XIII edited characters,!
About VP, it's a good base!
I partuculary like Eri and Kaede's design... :

The only point woud be, VP sprites are a particulary style, so it's difficult to mix it up with enemies from other games...
So the enemies will look all the same... Cute girls only. :-\
If only a game with simillar graphics exists with monsters and bigger enemies on it... :

I don't know about exact size, but perhaps using some blazblue characters as enemies can make it
But, again, do it, it's one more thing not yet made with openBOR.
(Sorry I don't find the Spoiler button)