I bought a second Dragonfly 2. I had the funds, I love the steel(HAP-40), I love the platform, and since it's a sprint and hard to find, the important factor was that my local B&M held one for me. Otherwise, I don't plan on buying duplicates. I don't have the money, and I'd rather go for highly-curated diversity. That said, there are knives that I would probably own multiple examples, such as various PM2s, or another sprint run of a knife I already have. I also don't count knives in the same family as duplicates, like the Sage or Chaparral. The exception would be if I was able to get a really good deal on something, and if it seemed like I'd be able to possibly unload the extras(like if I found Caly3s for $100; I'd buy two or three and sell all but one).
I will say that I wish I WAS in a financial position to be able to buy duplicates like that.
Current: Dragonfly 2 ZDP-189, Chaparral 1, Techno 1, Delica 4 HAP-40, Dragonfly 2 HAP-40, Mantra 1, Ladybug Salt Hawkbill, Nirvana CPM, Endura 4 HAP-40, Sage 4, Para Military 2 CPM Cru-Wear, Sage 5, Caly3 HAP40, Sliverax, Lil' Nilakka, Chaparral Raffir Noble, Zulu, Manbug HAP40, Meerkat HAP40, Sage 1/Sage 2/Sage 3 CF, Introvert, Techno 2