I have a 4G Xoom, so I can not give comparison of which one to get, but I would fully support getting a discounted Xoom and would not hesitate to buy one today if I needed one. Even though it is 18 months old, it still operates great. It does everything I wanted, and I still am finding ways to use it.
The issue between WiFi and 4G. It all depends on what you want out of it.
I originally chose the 4G because I wanted the ability to use it anywhere. In reality, I only use it for about 200 MB each month, as the rest of the time, I am on wifi networks.
4G is still on ICS (which I really like on the Xoom, but absolutely hate on the Razr MAXX), and it works really well.
WiFi has already received JB, and it seems receives it very quickly after release, since it is a Google Experience tablet.
Either way, I think you can not go wrong with the Xoom, if you want a cheaper intro unit (due to being a little older)