In reply to A Longleat Boulderer:
Use the Advanced Search on Mountain Project to dial in the boulder problems you are looking for. Here's a quick hit list of V4-V9 problems with >2 stars:
https://goo.gl/WvRYkq
In terms of sights, unfortunately Mariposa Grove is mostly closed until 2017, but you should definitely check out one of the other giant sequoias groves on your way into or out of the park (
http://goo.gl/z65KuQ). Those trees are insane.
If you bring your harness+helmet+shoes you can definitely rope up with someone. Simply go to the message board at the Camp 4 kiosk and take your pick of people looking for partners - or post a note yourself. You can also just meet boulderers that way - preferably boulderers with crash pads.
Depending on temps, the resident black bears can be active in March and I've definitely witnessed them in late winter pealing off car doors to get at a bag of chips ("crisps") left inside. So be aware of what you leave in the camper if you stay in the valley overnight.
In terms of sleeping spots, Camp 4 is a great place to camp and meet people from all over the planet. If you want to sleep in your camper, however, there are lots of unofficial camping spots just a quick drive down the road toward El Portal (there's a kayaker spot just past the town of El Portal that is super cool, kayakers always seem to be in an awesome mood). You can try staying in your camper parked among all the El Cap cars, you just have to keep the lights off, close the curtains, don't make a sound, and never give up that you're actually inside (no matter how much the rangers bang on the door and shout "we know you're in there"). I'd go with the Camp 4 option, it's the most fun.
And no matter how tempting, avoid the food at Curry Village. Grrr, the "curry hurries"... not fun.
Have a blast.
Erik