You can have two 360's and play XBLA games online as long as you're using the same account. I have two 360's as well and I constanly use them both (I keep my profile and most save games on a USB drive).
I believe the license transfter is only moving games from one 360 to the other without redownloading them. So if you bought an XBLA game today, you could download it on both 360's without a care assuming you're using the same account.
The only thing I'm not sure about is having the same profile signed on it multiple places since I've never really needed to try that.
-edit-
Note that if you do bring your other 360 online without keeping your profile on a USB stick, you'll have to do the annoying profile recovery every time (it's all automatic, it just takes a few minutes to do which makes it suck). It's not that hard to keep a USB stick in a 360, though it means one of your USB slots are always taken so I don't know if that's a problem for you.
