I do not see why it is not a good time to purchase one honestly. Sure you can wait for something better, but is that not always the case with all technology related components these days? It has dropped some in price since it was released, and again sure, it will drop more when new products are released, but again, if you always play the waiting game, you will find yourself in an infinite loop of waiting for the latest and greatest to be released.
As far as it being 50 dollars more than any AMD offering, well for some people, that extra $50 is worth it as far as driver support and the other things Nvidia offers, like the GeForce Experience. Note, I have not used that Experience yet myself, just saying, $50 is not a ton of money if what you are purchasing has better support than another similar brand. Now obviously that is an opinion based comment, but I think it is the overall opinion of all that use it that Nvidia has always been good with their driver support, etc.
Actually, if you're looking midrange (and thinking AMD) now is an ideal time to buy - the HD7850 in 2 GB trim is basically a high-end card in midrange clothing. Most of them have no more of a power requirement than the HD7770 (which has half the RAM) and cost little more (and take up NO more case space). Where AMD has had their issues is in the multi-GPU space (and especially compared to nVidia SLI); however, unless you are driving multiple displays, you'll only need a single HD7850 2 GB - even for Crysis 3. However, I've never been a fan of multi-GPU in ANY case (whether CrossFire or SLI) - the only multi-GPU I'd ever done is back in the 3dfx days - and, as is the general case with multi-GPU today, only certain games really took advantage of it then (and it's still largely the case today) making it, at best, an outlier feature.