Hi Penny:
I'm afraid I will not be much help in this decision as we do not have a Wii, but DH and I decided awhile back to get a PS2 and a few games we could play together and after the first day out of the box, it sits on the shelf under the TV collecting dust-bunnies! We haven't touched it since. Now, as I said, I don't have a Wii, nor have I seen the Wii fit, or coach you referenced, but I too would feel a bit wierd standing on a little plastic square watching a cartoon of myself on the screen doing whatever... I do have some friends that are more active, have lots of parties/company/family to their house and they use the Wii constantly for the interactive games... Tennis, bowling, baseball, etc. that require other features than the ones geared towards fitness. The beauty of this is the "interactive" part of it though! They have even complained about having DOMS after a long session because they aren't simply sitting on the couch using their thumbs and trigger fingers, they are actually up and moving around. I guess it will just depend on what your goals and lifestyle are... if you have always wanted one, and think that you could get into using it several times a week, then keep it... if not and you think it will (like ours) eventually collect dust after the shine wears off, then by all means spend your money elsewhere...
Does your DH like to play games and such? (I sometimes feel that they buy US gifts they really want for themselves...) I have a feeling that I got a camcorder for Christmas... Never asked for one, never mentioned it in any way, nor will I ever use one (heck, I have a hard time using the $500 digital camera I bought a few years back!) but I KNOW he has wanted one for awhile now because he wants to put some music clips on his guitar forums and MySpace page... funny how that works...
You have a tough decision to make... Hopefully some more Catheites will have some more hands-on experience... for me, (not having any kids either) would opt for other means to achieve my fitness goals.
Good luck & Merry Christmas!