We try to build a little bit of time to ourselves into each trip, actually. Family trips inevitably requires compromise at just about every turn, and knowing that we'll each have a few hours to do whatever we want without regard to the rest of the family's wishes makes those compromises much easier to make. Also, it is astonishing the amount you can get accomplished when it's just you. I tacked on an evening at DLR to a business trip last summer, and I got an incredible amount done in just a few hours.
I ultimately prefer experiencing it at all with my family, but I would not hesitate to take a short solo trip if the opportunity presented itself, and do enjoy having some time to myself on trips.