Fan-of-Fans: I agree!
I think acquiring a filthy machine and cleaning up, returning it back to the way it was suppose to perform and look is part of the fun. It gives our hobby an "activity" and something to actually do with it.
Comparatively:
Lets look at Baseball cards, coins and stamps.
Yes, they're neat. But you get them, clean off former owners finger prints, on coins they may need soaking to restore the original shine. After that they all go in some sort of box or album and just sit there. You can't use them for anything, can't repair, play with or alter them. It's essentially a once and done hobby with each piece that one would take in.
With vacuums, it's a bottomless pit of what can be done. One could swap parts, alter the color, try different brush rolls. It can go on a shelf for display or be used on a daily basis. There is actually something to do with it to keep us busy which essentially is what a hobby should be. Something one enjoys doing in his/ her free time. If a machine is filthy upon being found then it might go into a shed, garage, basement until ready for the main house.
There are car collectors who take in filthy, rusty vehicles. Some of them don't even look repairable! Those need the same process but in a much more time consuming, expensive way and not to mention a vehicle takes up a lot more space than a vacuum!!
In terms of smells and odors. I was trained at Rainbow and Filter Queen that the smell is a result of a few weeks worth of dirt that has been stored in a vacuum cleaner bag. If you think about a vacuum cleaner, it is the perfect breeding ground for germs and bacteria. There's dirt in the bag, it's dark inside the bag, especially if the vacuum is stored in a closet, it's warm inside the houses where vacuums are kept, the dirt is surrounded by surrounding dirt and germs so it's a breeding ground inside of a dirt cup or vacuum bag for dirt and germs to reproduce molds, fungus, bacteria, dust mites, etc. The smell produced from a vacuum is a result of that mold, fungus, etc. A home with pets is generally more susceptible to it because of the animal dander now being picked up.
The more often a bag compartment is wiped down, filters are washed or replaced, brush rolls are kept clean, and bag or dirt cup is emptied or replaced the cleaner and less or non-smelling a machine will be. Normal consumers don't care for their stuff and that's when odors get awful!
It's those machines where the brush roll is so coated in hair and junk that one can't even tell what color the agitator brushes are supposed to be because they have become invisible! Or the vacuum bag was installed improperly so the pre-motor filter is completely clogged, yet the consumer doesn't even realize that a pre-motor filter even exists or what it's purpose is nor what the original color is supposed to be of the pre-motor filter!
