Given your time window(I'm a huge Mexico fan & just got back from Baja) I'd take in the rocky mtns for as long as your time & money holds out and do the west coast too if it's important to you & it is a neat area to ride. Plan around the time the highest elevations offer clear riding & camp & hike(to Really!!! see the mtns you must walk!!!) while there for sure. Skip Baja for those dates unless your into big fish at high boat prices. Memorial day on should get you most places in the mtns..
"If I had my life to live over,I'd dare to make more mistakes next time...I'd relax,I'd limber up.I'd be sillier than this trip, take fewer things seriously, I would take more chances... take more trips...climb more mountains...swim more rivers...eat more ice cream." Jorge Luis Borges, at age 85