I was in a similar boat as you during the spring sale - have a powerful desktop, was pondering getting the deck. Decided to go for it and to be brutally honest, it’s mostly a new shiny toy, not a revolution - which is absolutely fine enough.
I am excited about it, enjoy using it very much (on a long train/bus ride, on couch/in bed), but I don’t use it every day, it hasn’t been some miraculous revelation. However, it built a new clear division for my library: on one hand smaller, less demanding games I now save exclusively for handheld experience (thanks to this I already tried some games I probably wouldn’t on PC, at least not in near future), on the other for big, graphically marvelous games still prefer a big screen.
Also, if the desktop goes unexpectedly tits up some day, it’s nice to know I have an emergency solution in the form of the deck.
Seconding It Takes Two, a fantastic game. Played with GF who’s not gamer at all, enjoyed the hell out of it.