$250 new for a $400 grill, yeah, that's worth it in my book. New model probably has some features and enhancements, but $150 off is not bad. I got the Q200 instead of the Q2000 and it was used, an even better deal for me.
I bought my Q320 used, also have a Q300. That sounds like a good deal on the 320, you will really get a lot of use out of it and will enjoy it for years to come--
The price is good, I agree with everyone and go for it. I love hearing people reselling their Webers. They are built to last and everything can be replaced if need be. Enjoy your new (to you) Weber !!!