Without reservations, Yosemite will be tough. Heading in around Vegas and then going northward might give the mountains a little bit more time to melt out.
In response to your question about heading north, Lassen is worth a visit IMHO. Some thermal features can be seen with short hikes from the parking lots. About half the sites at Manzanita Lake are walk up (meaning no reservations taken) so one can often get in, esp. mid-week. However, the road through Lassen can be closed by snow until well into June.
Further north, Lava Beds NM is quite different. Nice little CG. All sites are walk up. High desert, so free of snow much earlier. Interesting history and geology. We happened on this place some years ago when snow up high forced us to change plans. We plan on going back again sometime to explore with more time.
