How much of RPVX can be converted to use in VXAce?

I'm thinking bout transferring almost all of my project into the new platform but I would like to know how much of the files used normally for VX can be transferred over for immediate use.

What do you mean by transfer? Do you me simple Copy and Paste, of each individulal map/event/database entry. Or do you mean copying over the files from inside the game folder, either or...in simple terms, it doesn't work, however there is an option to use VX style mapping in VXA, by using the Area Type option on the Tileset section of the database:

There are programs that will help you convert maps and events over to Ace, but I've heard mixed things about them and don't know how effective they are. Scripts can't be transferred, though.