An SUV such as the Xterra will be better suited for your family and intended uses instead of a Wrangler. A Wrangler doesn't have much cargo capacity when it's carrying passengers.

It doesn't sound like you'll be driving ON the beach, just to/from the beach with your family and a wet, sandy dog.

You can get pet dividers and vinyl cargo area liners for the X to keep your canine companion in the rear and not ruin the rest of the interior. I've got a dog who loves to play in the ocean and go camping with me, too, so I know the value of an 'easy-to-clean' machine.

If you're not intending to really use 4WD for any type of "serious" off-roading, you might actually consider looking at the Honda Element as well as the X. My wife and I recently looked at one while looking for a replacement to her 93 Accord coupe, and we were actually impressed by it. It has a lot of interior space, the rubberized floor looks to be really easy to clean, it handles well, and gets pretty good gas mileage, too.