Upgrading from a standard 47" Vizio to a 55" 4k Vizio - worth it?

[IdeaOfEvil]

I'm not one for gimmicks (3d, curved screen, 4k), so I don't have any players or discs that can take advantage of them. But I am going to be buying a new tv very soon, and I'm wondering if I should pay the extra $150 to get a 4k tv instead of just a standard screen.

Thing is, I have some gift card credit with Amazon that I'd like to use and I can't make heads or tails with what they have for sale. There's a 55" Vizio E-series (I'm guessing E is for economy) that has good reviews but less hdmi ports than I want. Then there's a 55" Vizio 4k 2015 model for $100+ more with enough ports and just as good reviews.

I have about 4 hdmi devices I use - region free bluray player, ps4, my pc, and a ps3.

My basic questions are:

-Is getting a 4k tv better than not if I don't have any 4k content to watch?
-Are Vizio's still good tvs?
-My budget is around $600 (give or take); should I look at a different brand?
-Is 55" too big to upgrade to if I only have 1080p/720p content to watch?
-I won't be mounting this to a wall, so are the legs a problem being spread apart versus screens that have a center placed stand?
-Is buying a refurbished tv a bad idea?
-Since one of them is listed as a 2015 model, should I be looking for a 2016/2017 model?
-Is there anything else I should consider that most people overlook?

Thanks!