I've attended NJPW shows, yes... but only at the Tokyo Dome and at Yoyogi Stadium in Tokyo. Never attended one in Sapporo. If you're into wrestling, absolutely do it, you won't regret it. That said, be prepared to give up your mid-afternoon to late evening to do so. If you have limited time, you'll have to judge how much you like Japanese wrestling haha. Seeing NJPW live - the wrestling is very high quality.
I would do it if I were you.
Also, visit
https://buysumotickets.com/ if you'd like to get tickets to an NJPW show. They do all the work to get the tickets, and they're super helpful. It's nice to have that stuff all arranged before you go. I've used them twice now, and they're 100% reliable.