hmmmm depends, depends, depends...
It's 33 miles, so if you are pretty quick you can finish it in a 2 - 3 hours as long as you don't stop for a long time at all the rest stops. It is relatively hilly - I don't recall any stretches that I would call flat - so I'd say its rolling to hilly. The ferry ride is (I think - check the WA state Ferry schedules) 30 minutes.
I'd say go if - you want to get the experience of riding on a big group ride, before say the STP
Don't go if you've been there done that and are concerned about getting home in time.