MOVING FROM RPG XP TO VX FOR NEXT PROJECT...YES OR NO?

For the first question, you'll have to make the 3x4 grid instead of the 4x4 that XP has going (animation wise) but the sprite sizes should be fine the way they are. For tiles you'll have to make up sheets (simple cut and paste for the most part, though autotiles are a bit harder to work, I think).

As for what it can do... well, a lot. Anything that can be done with Ruby is applicable (you should probably check out some script areas on different sites to see what there is to offer in that department). The database is where it really shines, though.
You can create custom damage formulae and all kinds of crazy stuff by just using the database and your imagination. For example, a character who double weilds, absorbs ice and thunder, deals crits, is targetted by the enemy more than others, has the chance to do multiple attacks every turn, and learns skills that do damage based on their Speed instead of attack.

It's very flexible in that way. Characters and Classes have Features lists which allow you more customisation over your creations as detailed above.

The major downside that you'll notice is that the mapping is set up a lot more like 2k3 than XP. There's only two layers (granted, you can use pictures/parallaxes/events as layers too) to the mapping - A and B/C/D/E. A layer forms the base/ground and BCDE are four pages that form the upper. That said, for the most part, mapping is easy enough to understand once you stop expecting BCDE to be separate layers.

It also runs at a higher FPS than XP and there's a lot of community support for the engine - legitimate support from Degica, too - just in case anything goes wrong or you need to know how to fix/do something. There's a LOT of scripts out there for free-use and plenty of assets as well - the resource packs are especially nice, though if you aren't using the RTP you probably won't want to use them that much.

Hmmm... the eventing is the usual. There's a few little bits missing that were in 2k3, but I'm not sure that they weren't missing in XP too, so I can't say much about it. Oh, but the windows are a lot better! That is, message windows.
There have been subtle changes to the event commands - things like Button Press Checking (instead of working around to check which is being pressed by assigning variables, you get an actual command to check which button is being pressed) and Key Item presenting, scrolling text, script lines for conditional branches and quite a few other little bits and pieces that are an upgrade.

Coupled with scripts it's quite a powerful engine.

Oh! And the help text is actually pretty useful. And if you hover over a command a pop-up will appear that gives you info on it.

There's also the generator but as you're using XP graphics you probably won't care about it.

If you really want to get a decent idea, though, there's a Lite version which is free. It limits the amount of maps/database items and such, and doesn't allow scripting, but it's basically got everything else that's in the full version which is more than enough to just do a bit of experimenting with. You can find it on the rpgmakerweb.com website. Just look for Ace Lite.

I would recommend checking out Princess Princess, Homework Salesman (from what I remember the emphasis wasn't really on fighting), The Grumpy Knight, Subterranean Starfield, and The Legend of Ace. They're all completed, from what I remember, and decent games too.
Reincarnation, X-Noir, You Are Not the Hero, A Tale of Valera and ReEvolution are some good demos, from what I've heard.