I've done 3 even last year. That was maybe a little much, the third night was a total "stop and smell the roses" thing. I actually ate during the third party, that is completely unheard of.

But I am a character person and had a lot of catching up to do, I definitely don't regret it.
I got lots of stuff done that I would have missed out on. Finally met Megara after all those years (her line was already closed first party, she only came out late when we had already left the area), caught Merlin who wasn't out the first night, and my friends swear I positively melted when I got the chance to chat with Scarlet Witch for a while and she actually remembered even my name from last time I visited. I had a Wizard Duel with Madame Mim and became her new best friend. For me that was heaven.
Definitely planning on at least 2 again this year.