Is it considered to be breaking the fourth wall to acknowledge something like imm exp, or alteratively ungrateful if you ignore it and keep playing like nothing happened?

People pray up a 'thank you' all the time. It's fine.

I don't think anyone thinks you're rude if you don't though.

One of our former immstaff considered this a big pet peeve of hers, when she'd award role XP and they'd pray a thank you.

I never really understood the problem, but it stuck in her craw apparently.

That said, I do not think anyone currently on the immstaff has similar issues.

So I think it would be kosher to throw up a politely OOC thank you.