I know you said you were going to CA already, but I'm assuming you're not taking the kids to wine country, so I was going to suggest Sonoma too. Sonoma, not Napa. Totally different feel I think. I thought Sonoma was more romantic and less touristy. We loved it and we also went in June-- weather was warm, but not too warm. Very relaxing, very adult! We stayed at a B&B that has since gone out of business, but there are a ton of good ones out there. Highly recommend the Benziger winery tour.
I was also thinking, why not Puerto Rico? It's in the U.S. so no passport required. It's not rustic anymore. :-) I have never been there, but I have several friends who vacation there and they love it. They have all-inclusive resorts there too.
The other place I was going to suggest was South Carolina-- the beaches there are amazing. We went to Kiawah Island last year in late May and it was incredibly beautiful. The only bad thing is there are lots of bugs-- mostly palmetto bugs though (a polite term for cockroaches). But you really cannot beat the beaches, the golf, the scenery. It is AMAZING! And it is NOT crowded like Florida. They have a resort on Kiawah that is incredible. Expensive, but incredible. We stayed in a rented house on Kiawah, but we did visit the resort. We rented bikes and rode around the island... there are bike trails everywhere. We really had a wonderful time.
Good luck and have fun!
I've been to Chicago a few times, and I wouldn't put it in the category of relaxing or romantic... :-)