Upgrading cartridge used or new?

It is a gamble and would be a hit or miss.
I've bought 5 or so used cartridges/stylus in the past 10 years, and 4 were pretty good and 1 was defective. Still, I paid for less than a third of the new price for each, so it worked for me.
The most important thing is to buying one from an honest and reputable seller.

Those of us who buy second hand know, or should know, what we are doing, risking. As Ilcho says, the rewards can be very great indeed, 33% or less, of the retail price, for a cartridge not even run in yet. That's worth a bit of a gamble, for me anyway. If it's not worth the risk to you, that's fine too. More chance for me to snap up a bargain

How many of the members who avoid used cartridges have actually worn out a MC cartridge, or had the suspension fail and of those, how many hours did they get out of their stylus.
I'm not interested in what you have heard, or recommendations, but actual failures due to wear, not breakage.

I have never had a suspension failure. I used a Koetsu Rosewood almost daily for 3 years and absolutely wore out the stylus, about 3000+hours. After a $250 retip, it sounded as good as new

I had one that I bought new that wore out in about 5 years. It happened so gradually that I didn't really notice it until I changed to another less expensive model cartridge in the same line. Then I tried to re-mount the old cartridge again and it just didn't sound good at all. I don't have a microscope, so I can't say if it was the stylus of the suspension that was the problem, it just sounded lifeless and sluggish compared to the new one.

I also remember buying a used cartridge that I thought just didn't sound good to me, so I turned around and re-sold it, like I do with other gear that I don't care for the sound of. The person I sold it to told me that it was shot, that he could see under a microscope how worn the stylus was.