Pretty sure this is a simple question, but one left ultimately to you.
Essentially:
Is the Droid X user experience that much better than you're rooted Droid experience that you would spend $100 on it?
The DX is obviously the better phone, and if you have $100 to blow, then why not? I wouldn't do it personally, but that doesn't mean you can't... I'd rather wait for the next leap.
Maybe the better question is: why does he want your Droid more than his Droid X?