They're going to spend every 5-10 years when the bulb burns out or the caps go or the kid chucks a Wiimote through it or they just feel like treating themselves. 4k sets are already $6500ish for a 55-inch in Japan; (yield-based?) issues with an overseas launch aside, in a couple years they're going to be a standard premium product, and by the end of the next console gen 1080p and 1440p is going to be like 720p now--you're going to be hard-pressed to find it in anything but low-end laptops and TVs that come in a plain cardboard box labeled "TV".
As for what exactly new consoles do, 4k is likely to be MORE useful if they cling to 720p+effects; a big advantage of 4k sets is that they can display 720p pixel-tripled and 1080p pixel-doubled, rather than the terrible vaseline effect you get from consoles now where the console scales from 3/2 anamorphic 540p to 720p and then your TV scales from 720p to 768p or 1080p.