Re: Las Vegas or San Diego
If LV is on your bucket list and you can get a sitter, I'd go there. I've personally never been and don't have much desire to visit Vegas but I'd much rather go to a new place and if it was on my bucket list, it would be a priority for me.
That said, with or without kids I LOVE San Diego. So much to do and just a beautiful atmosphere and laid back culture! Love it!