I had really high hopes but low expectations for Tap 2, just because it can be really tricky to follow up on a cult classic without totally stepping in it. I drove way out to see it on IMAX, and the entire family loved it.

May Reiner, as they say, Tap into the afterlife!

What is the benefit of seeing a regular film on an imax screen? Just bigger (too big?), or do they have taller footage?

Don't exactly know the difference in footage. I will say that I was on the fence about whether IMAX was a big deal for Spinal Tap 2, but afterwards we all felt like it was worth seeing in IMAX. Part of why I saw it in IMAX is that it was an early showing (IIRC the day before official release) and the IMAX theater 30 minutes away was the only option for seeing it that night.

The primary reason it shined in IMAX was the concert footage; It's giving "I'm on stage at a Tap concert".