We did one extra day and took out at Spring Bar last year. I was afraid that the last day would suck, with the road across the river, but it actually turned out great. It was a fun, casual end to the trip, and we had an awesome beach camp. The trucks & trailers on the road weren't that bad. From Carey to Spring Bar, there were no rapids of consequence. Beyond Spring Bar you will have day floater/commercial day trip traffic on the river. The closer you get to Riggins, the less private the camping becomes. There are several moderate rapids (class III?) between Spring Bar and Riggins.
Have a great trip. The Main is my favorite.