Unless you sit really really close you won't see any difference between 2k and 4k content.
The new TV may look worse than your old one because regular FHD will have to be upscaled and that is expensive to do well.
The 4K TV you link to doesn't have HDR which does make a very noticeable difference in contrast and color.
Upcoming tech includes dynamic HDR, DolbyVision, HDMI 2.1, and ATSC 3.0 4k HDR over the air broadcast tuners.
Waiting can be a good thing.