I resolved my indecision regarding a Hilton Lakes backpack and car-camping by a hot spring...by backpacking up McGee Creek, driving to Mammoth Saturday and doing a one-night trip to Steelhead Lake on Sunday.
I've seen better fall color in the eastern Sierra, it seems like color is proceeding quickly from the yellow phase to brown. Probably the best example of this is in Lee Vining Canyon, at the first sharp right curve after Ellery Lake where the trees on the left (west) side of the little stream were fading and the trees on the right side were part green part yellow.
It turned out McGee Creek had some pretty reasonable color, and I had Steelhead Lake to myself on a Sunday evening.
There's plenty of water in McGee Creek, and in all the freshets flowing into McGee. The USGS map shows most of this being spring-fed, that appears to be the case, even in a dry year like this water is plentiful there.
Pictures.
A few pics...
Along the trail:
Larger view of same area:
Steelhead Lake:
View of Grass Lake from climb to Steelhead: