A LOT more from Guadalupe than from Oceano (far fewer 4x4s). I lived in Guadalupe for 5 years and my late father-in-law used to guard the gate to the dunes there in his early 80s (he never quite got the hang of retiring).
I found the dunes astonishingly hard to photograph. The canyons a few miles inland were easier but still difficult. Don't miss San Luis Obispo.