OP here. To answer some of your questions... They're not abusive at all and really not awful either, but:
a) I just don't have much in common with them.
b) We did a long vacation with them a few months back and I feel like I got my fill then and am still kind of recovering.
c) Being at their house is worse than vacation because they are very particular about how everything is done and treat you like a 13 year old.
I'm still undecided but leaning towards not going. They know my work schedule and that I could make it, but I think it's fair to say I just need a break and am not up for the travel. Hopefully they'll understand and if not, oh well. My husband will likely get some crap from them but he understands where I'm coming from; he'd be disappointed but it wouldn't cause major issues in our relationship.