Neil -
I rode my Navigator all through 2004, '05 and '06. It handled the C&O very well and was a joy to ride. It's a little slow and cumbersome to take on the road, so in late 2006 I bought a Novara Randonnee. It has 700x32 tires. I loaned my Navigator to my daughter's friend, ****y, and she hauled the trailer with the girl's gear in it... until the girls met some teen-aged boys full of energy and then *they* hauled the trailer.
Anyway, I digress.
I like the Randonnee, and I like my Navigator. The Randonnee because I could load most of the gear for Libby and me in panniers and not have to worry about a trailer; the Navigator because it could handle anything the trails could dish out and was stable. I lost it twice last year - once near Cumberland in some grass on a hill, and once on the detour on a gravel road. I discovered that unlike the Navigator, the Randonnee isn't a tank and you can't just plow through obstacles, but it was a nice ride too. (I did lose it with the Navigator in 2004... around Dickerson when I hit a nasty mud puddle (actually a four mile stretch of mud puddles) and landed face-first into a patch of stinging nettles). We hit a dry spell in mid-to-late July last year when we did our trip. I don't know how 32cm tires would handle mud puddles, I guess pretty much like the Randonnee handled loose gravel - not too well, not very stable.
For the most part, I found that the puddles are not bottomless and *usually* if you steer into the center of them, it's not as mucky as trying to steer around them.
As far as being heavy - my guess is that you and I are near the same weight range, but my vote is "because it's spring and the ground is too soft".
Judy