I played at Xtreme this weekend and actually had a blast.
But you're right: the turf was disgusting. Made for easy sliding though.
I wanted to go up to Action Center last summer but didn't have time, though I have called and spoken with the owner and, as you said, they allow walk ons to join the private games. Maybe we can plan a trip this summer and get up there. Maybe Magmoormaster would be able to go?
You should definitely come down to the Hobble Creek games; not Provo - Springville. The field is up Hobble Creek Canyon. The field is small - frankly, it's speedball in the woods - but it's a fun field with a great crew that runs it.
I've played at Squaw Peak a few times but I think it is basically off limits now.
There is also the field in Eagle mountain (google maps...search for eagle mountain paintball field and someone has marked it lol). That field is in a state of disrepair; I don't think Team Desert Edge maintains it anymore, but there are still some pretty big bunkers and lots of cedar trees to hide behind. And sand. Lots of sand.
I organized a game there over the summer, though it's still a drive for you.