This is my all time favorite subject!
Keep it coming. I have two HDs (yes, I'm blessed with a good family, friends, and job(s)). When I bought the Road King, I just had to have all the do dads, shifter linkage, passenger footrest covers, eye lids over the lights, new handlebars (bought the ones that I could keep the cables stock - like I said, I'm cheap!), fairing lowers, pressure gauge, and oil temperature gauge.
But I haven't touched the engine (yet). Why? Again, I guess I'm just plain old cheap! And, my old man, a pretty handy mechanic used to tell me this story when buddies of mine in HS were souping up their cars. He'd say "so, do you think these guys can engineer better systems than the guys working on this stuff daily at Ford or Chevrolet for a living?". That always stuck with me. Also, I seem to remember driving right past the guys on the side of the road with the souped up cars after a few months of racing around. Sort of like the tortoise and the hare I guess...
Anyway, I am still keeping my Ultra Limited completely stock as long as I can. Marketing in America is a strong and hard sell to ignore, let alone peer pressure.