I think 4k is smart from a marketing perspective. With the new 4k next gen systems coming out, if Nintendo can say hey we too have 4k on the Switch at $300 with a huge library of games already available, you can get 4k on the hottest system with way more games and cheaper than the other 4k systems.
I think whatever other upgrades it has will be bigger sellers than just the fact that it does 4k, but for some graphic-focused people it might help them finally make the leap to Switch, and for current Switch owners that have a 4k TV it'll add that little bit extra incentive to upgrade so you'll get more people double dipping on the Switch, and it'll just be good marketing to say Switch has 4k just like these expensive new systems.
That's definitely true, most people who buy gaming systems are far more casual than we are and don't really pay attention to gaming or specs like us. Once they see the word "4K" they aren't thinking about whether games will only be upscaled to 4K or fully rendered in 4K cause they don't know those two things even exist or are entirely different from each other when it comes to graphical capabilities. Once they see the words "4K Switch" they'll get excited that they could get the hottest system at 4K for potentially only 300$. 4K is a big marketing word now even if games on Switch won't even render games even close to 4K.