Erm... sorry, gonna hafta disagree w/you a bit here - what these builds are "meant" for is completely up to the builder.
"Show and tell & gas mileage... to just have fun" is indeed part of it, but hardly the whole story for everyone. Some are
built to "win a race" http://motorbicycling.com/f35/death-...1-a-26743.html
...and those guys help the rest of us with their innovative ideas and advancements, same as with other motor vehicle racing.
I personally ride a "cruiser fat tire single speed vintage bicycle" (tho it's a single speed no longer) http://motorbicycling.com/f38/rustor...off-13144.html
and although I do jus' "cruise" from time to time, I assure you that's not
what I built it for lol - I spent way too much time tweakin' the motor to jus' putt around at idle speeds
I use it and my mountain bike as daily commuters, averaging roughly 6000+ miles a year between them - the Schwinn mountain bike is the winter beater & trial hog, also not exactly just "cruising" as it spends waaaay too much time in the air or sideways to meet that definition heh
"Having fun" is w/o a doubt the most important thing, but that's jus' the start - the "what and how" of the ride is as diverse as our memberbase... and honestly, that's one of the things I love the most about these things