Definitely take the fenders and rack off. Put some knobbies on, practice some dismounts and remounts, and sign up. It's fun. A lot of serious road racers do cross, but most don't take themselves very seriously. It's definitely a good time. I wish I was able to do more cross racing, but I have two kids playing soccer and it's been tough to find a free fall Saturday. (That, and I gave my SSCX to my son to ride to school, so I need to get a new CX frameset. Oh well....)