I went down from Eugene last year for 4 stages, it's much more than the racing, it's a huge party. If you can swing it go to Santa Rosa for the stage there, it was the most fun last year for me, plus there is great riding in the area in the morning before the race activity starts. The race in Sacramento takes over the Capitol area of downtown, it will be a fun time, and should be excellent racing if it isn't raining.
I'd say go for it, it's a great time!
It can be a PITA but check Amtrak. But driving allows you to take your bike if you'll have time to ride.