When I first started taking photos, one of my main subjects was motorcycle speedway. Two teams, one track - about 400 metres long, 4 riders to a race, lots of cinders flying, 500cc single cylinder, run on ethanol, no brakes, skid round corners and lots of crashes.
I had an old 35mm Edixa with a WLF, 50mm lens and a 300mm f5.6 "Prinzflex" which was pretty crap - but all I could afford. I wasn't sufficiently savvy to put filters on the front of lenses as a teenager and, as a result of repeated exposure to the speedway track (or at least part of it) hitting the front element of my lens, it got badly scratched but still kept producing half-decent shots. However, eventually it got so full of crud that the focusing became completely jammed and I couldn't get a bean for it and threw it away.
Which sort of brings me to my point. I like lenses which have flawless glass and mechanics - especially if it's an auto focus lens (yes, I use them). I'm less exacting about the cosmetics (within reason) but I expect lenses for which I've paid good money to work as they are intended and have some residual value if I decide to sell or trade them.
Maybe that's why I've owned a couple of Leicas down the years......