I love IMAX, but if you don't have a full-size IMAX then it won't feel like much of an upgrade. Thankfully, my IMAX is the AMC Metreon which is one of the largest in the country. I feel like I get the full treatment anytime I see something there.
For 3D, I've given it plenty of opportunities to win me over. A few of those experiences felt really worth it -- mainly Beowulf (the first I ever saw in IMAX 3D, and it was really well suited for the format) and a handful of animated films. The one documentary I saw in 3D, Herzog's Cave of Forgotten Dreams, did feel more immersive but also suffered from some strange artifacting in the image (camera picking up dust in the shots? I can't really tell what the issue was) which made it distracting. Most other 3D experiences didn't feel additive and in most cases had varying levels of distraction.
Then there's the issue of the glasses. The last few times I've gone to a 3D showing at IMAX, the glasses are incredibly foggy and scratched up. When you put them on you see a fog halo the entire time you are trying to watch the film. Cleaning the lenses does nothing, and exchanging them didn't help. Theaters just aren't putting care into maintaining their 3D glasses.
When I don't feel like springing for IMAX or Dolby, most of the time I'm perfectly fine just seeing something at a normal 2D screen. These days they are almost all 4K digital screens, so everything looks super crisp. Sound systems do vary, but most are lightyears ahead of what they were a decade and more ago, so it's not a big deal to me.