Based on what happened to my wife, if the password was encrypted, breaking it was trivial

She probably had an account that had a very low number of iterations. LastPass never updated those unless someone knew to do it manually, so if it was an old account she likely had 5,000 iterations out of the recommended minimum of 100,000.

It wasn't an old account. It was made within a year of the breach.

just checked, mine is 5,000

Yep. And the sucky thing is that the only recourse at this point is to reset all your passwords, because what was leaked was the low-iteration vault. Changing it now only saves you for future leaks.

I believe that my vault was similarly-low iteration, however my master password was an approximately 30 character string that contained no dictionary words.

Based on your understanding, does my master password length sufficiently mitigate the low-iterations, or is decryption a realistic possibility?

If your master password has enough entropy, you're safe with 1 iteration. It's not a great idea, and what "enough" is can be ambiguous. But if your master password is provably 70 bits of entropy or so, you should be fine.

But it's probably easier to just change your passwords anyway. At this point I wouldn't be suprised if the story gets even worse somehow.

I don't know enough to know. I'd change your passwords just to be safe.