I guess I am Babar the Barbarian. I fly unpainted rockets routinely. I am more an engineer than an artist. In my defense (if needed!) many of my rockets are gliders and helicopters which fly better unpainted due to weight considerations. Most of my other rockets are engineering experiments where I am checking to see if the design works, not if it looks purdy.
Presumably the point of the hobby is to have fun. If fun for YOU is building something and getting it safely into the air as soon as possible to see if it works, paint is for the most part superfluous. If on the other hand craftsmanship and cool factor is important to YOU (or if you plan to display this proudly in your home, school, church, synogogue, mosque, or other important place), than paint is essential.
For a noncompetition sport rocket, any improvement in performance added by painting is, in my opinion, minimal at best.
I have seen many just absolutely gorgeous painstakingly handcrafted rockets that must have taken numerous hours (and probably weeks or months) to build posted here destroyed on their maiden flights. It's enough to produce cremasteric spasm (medical term, if you don't know what it means, don't bother looking it up.)
So decide what is important to you, the buyer/builder/flyer of the rocket, and don't worry about what anyone else says.
One consideration, if it is small and going to go high or be hard to find, a bright colored paint job or a very colorful parachute or streamer is REALLY nice when you go HUNTING for the rocket after it comes down.
Enjoy your rockets!
(Addendum: I do not bicycle naked!)