My bike is completely legal because if I get stopped and done for infringing the rules I will kick myself. I personally don't see the point in small number plates because to me the legal one is simply a number plate and making it smaller makes it no more appealling to me. If people want them , fine.Aslong as you can read it from the regulation distance, no probs.If they get done for it though they knew it could happen when they fitted it. To me the cons outweigh the pros.
Exhausts are a different matter. I like them
Having said that I'll still go for a road legal one as I believe some give that deeper sound that I like and are still Plod friendly. I still think they can be too loud even though I personally like the sound.
In short, I choose to remain legal coz I don't want the hassle of being pulled but if people choose to go the other way it's up to them but they know the risks.