Crowded or not, you can't beat the valley for easy access to wonderful scenery...not that there's anything wrong with Crane Flat, but if you stay in the Valley you can easily park and stay put for your 5 nights, hiking and seeing everything around on the easier trails. Really, the only real crowded ones I've noticed are Lower Yosemite Falls, Bridalveil, and the Mist trail, and all of them are OK if you go early. The crowds come from day visitors, and they have to drive in and park, so early risers get a nice quiet valley even in summer.
There are trails around the valley perimeter and to Mirror Lake and beyond that are relatively easy and enough to keep you busy for your 4 days easily. People tend to avoid the perimeter trails and often you see no one even in summer.
As far as North or Upper Pines, I've noticed a lot of larger RV's seem to prefer North Pines, and while most are nice folks, I prefer to be among tents when possible; Upper Pines also gets RV's, but maybe not so many. Both are well situated, but North Pines is next to the stables.
Gary
Yosemite Photo Galleries: http://www.pbase.com/roberthouse/yo