I took my two teenagers and one of their friends for their first overnight bike trip on the C&O over the weekend. We were on the towpath from Chain Bridge near DC to about the 50 mile marker and then back to White’s ferry. It was great.
I think it’s all about the bike and your expectations. Fat tires, fenders, and reasonable expectations for how fast you will be traveling can make it quite pleasant. That said, we planned the trip on three days’ notice and rode from our front door. If rain were likely we would not have gone.