I personally find HDR as one of the most impactful recent display tech, but there are plenty of hoops to jump through before you get to that experience.
You need a real HDR display (800 nits+), FALD or OLED for contrast, some calibration, and software that uses it well (really hit and miss at least on Windows).
Once all the stars align, the experience is amazing. Doom Eternal has one of the best HDR implementations on PC, and I suggest trying it once on a good display before writing HDR off as a gimmick.
There’s something about how taillights of a car in a dark street in Cyberpunk look, and that just can’t be replicated on an SDR display afaict.
Then you have some games where it’s implemented terribly and it looks washed out and worse than SDR. Some people go through the pain and mod them to look right, or you just disable HDR with those.
I’d vouch for proper HDR any day, that being said I wouldn’t expect it to improve Mario Kart much even with a proper implementation. The art style of the game itself is super bright for that cheery mood, and no consumer display will be able to show 1000nits with 99% of the frame at full brightness. It’ll likely look almost the same as SDR.