Well,......we are all different. This would be a boring world, if we are all the same. There is no vacuum on this planet that would make me tired of "pushing it", and I personally like heavy machinery.
My wife is a small, fragile woman (but handles a full size quarter horse just fine!), and she even doesn't have a problem with Kirbys. Our house is one level, so there is no carrying it upstairs (and if it was five level, there would be one Kirby on each level!).
I actually use the "massage attachment" to vacuum my large dogs, and it helps in between the weekly brushing. I agree that the "rug renovator" is junk (for MY needs), but in the household with light carpeting, and no pets, it actually works. Not as good as a decent extractor, but good enough to "brighten" the carpet. I haven't used other attachments to comment, and I would never attempt to buff (or polish) the car with Kirby anyway. Again,.....MY situation is different, and I have a fully equipped machine shop, with all the tools you can imagine (and some you can't!), so the "handi butler" is useless to me. However,.....for an apartment dweller, it might be VERY useful to have a gizmo that can be attached to the vacuum cleaner, and grind, sharpen, and buff, using the machine that's in the confined/limited space already.
In summary,.....Kirby is not for everyone, and there is no machine out there that is! It's EXACTLY what I like/need from a vacuum cleaner. I would never go through the "dog and pony" show to buy one (nor would I pay what they are asking for them either!), but buying them cheap, and restoring them, provides me with the ultimate cleaning machine for pennies, that I know inside and out, can source parts quickly, and will still be working when my grandchildren's kids will start cleaning their own houses.
My oldest Kirby (the one on the left in my avatar), was made in 1955, and my wife uses it weekly (her favorite). Since I restored it from ground up personally, I am sure it will run for another 60 years without a problem. Try to do this with Dyson!
The one on the right is only 10 years old, and it's not even close to needing any parts. In 50 years (when my daughter is 70!!), she can pay someone to restore it for her! And Kirby company will still be well and alive, with all the parts available for 100+ years old machines.