First, 4.2.1 and the Trip Planner look promising.
Second: This is on a Mac running 10.8.3, BaseCamp 4.2.1 (non-App-Store), and I have the TOPO 24K maps for the Western US from DVD (CA, WA, OR, NV) installed. I upgraded from a previous BaseCamp install.
So I decide to play with the trip planner for an upcoming trip to Yosemite, even though I know the route by heart. The way to Tuolumne Meadows from the Bay Area is simple:
I-580 out of the Bay Area, I-5 N, CA-120 E to Tuolumne Meadows.
Previous versions of BaseCamp with these maps figured this out.
When I used the trip planner (and later, the Route tool) to generate a driving trip, BaseCamp started promisingly, on I-580, but then sent me north to near Lake Tahoe and down the East Side of the Sierra on US 395 (not good), saving the coup-de-grace for last, putting our car on a trail over 11,000' Donohue Pass and down Lyell Canyon. Not only is this a foot trail and not suitable for cars, I'm pretty sure the rangers would fine me for not having a permit.
Routing preferences include avoiding "narrow trails" and "unpaved roads."
I have screen shots if you'd like.
