I like to have a good modern-sounding and looking kit. But I also like to have a vintage-looking and sounding kit, even if only for the aesthetic appeal that each possesses. Anything beyond that is too much, IMO.
I tend to agree with the opinion that it's really a personal thing. For some living in a small apartment 1 kit is all that is possible. If you have the room and the cash, 100 kits may be what you want.
As long as can and want to have that many it's perfectly acceptable.
Personally I have 8 in the house, along with a dozen or so snares...but all are utilized and my wife is really cool with them being here. If I had to sell them or the wife said it's her or the kits..........I'd miss her.
I also think that 3 kits fits all the *needs* of most drummers, while many can get away with just 1.
I'd say it depends on what you are doing. There are kits left at rehearsal spaces or studios. Maybe at a church gig where it can be left set up. Then there are the kinds of gigs you do. You may need a small kit for jazz or lounge gigs. If you play with multiple bands with completely different sounds and vibes, that may justify other kits. Maybe some vintage things for a trad blues band, a bigger kit for a rock gig.
I know a guy who has a giant set of Gretsch New Classics, all in the same finish. 20 and 22" kicks. 10,12,13 rack toms and 14 & 16 floor toms. He rarely sets up more than a 5 piece. But he can adjust to the size of the room or the type of music fairly easily.
The two bands that have rehearsal spaces already have kits there. So I just have the Safari kit for small things and a fusion sized D'Amico kit. I don't do rock, or at least don't in large places where it isn't mic'd and where someone would expect some huge arena kit. Besides, I'm not into carrying that much stuff around. If I can't do the gig with what I have, I'm probably not the right guy for it anyway. It might be fun to have some vintage kit like the black oyster Holiday kit I had 15 years ago. But I'm not sure how often it would get used.
OTOH, I do have 5 snares (just sold 2 so there's room for another or 2), 3 rides, 3 sets of hats and a bunch of crash cymbals which I rationalize as adjusting for different gigs instead of having entirely different kits. Nothing like some folks here, but easier to store.
Personal choice based on needs. Sometimes I feel like having 2 is a waste. I lived with 1 for 26 years and did just fine. The probably is I'm lazy now and hate to break down my home practice to do gigs, which is why I keep my 2nd in bags ready to go.
For me, owning 3 would be a colossal waste of money and space.
When I was into collecting drums I only ever had one set up, but there was a period I had 2 set up. Anyway, while I was still living with my parents rent-free I spent a lot of my money straight up on drums. I haven't seen my stuff much lately (they're stored since I can't play them where I live-- though I might be pitching in on a lockout soon, I might be able to play) but to my memory I have: (these are all player kits, some have mods or modern parts)
12/16/22 RB Gretsch blue sparkle (second favorite kit, I honestly forget if I have the matching 13" tom; previous owner rewrapped and filled holes)
12/14/20 60's Ludwig Champagne Sparkle (orphans brought together, my favorite kit)
13/16/20 60's Ludwig (custom rewrapped walnut veneer, dark stain)
12/14/20 late 60's Yamaha (one might call it light blue onyx)
12/13s/14/17 50's/60's WFL/Ludwig modded 'Imperial Lug Clubdate', Silver Glass
I might be completely forgetting one altogether...
Plus a half-dozen other orphans that I could make up other kits... some weird stuff, 14x14 Leedy, 14x24 70's Ludwig, 14x18 Keller shell kick w/ Ludwig lugs, 12x22 60's Keystone, I think a 12x15 marching snare I made into a floor tom, plus all my snares. I stuck largely to 50's/60's American drums. I also have another half-dozen or more shells or incomplete drums that need something to work.
I don't 'NEED' any of these drums, and they are a pain to move... are there too many? Sure, haha. but they are mine and I love them all. =) That's what's important. If you're not attached to something, get rid of it. I get pretty attached and sentimental over a lot of things so it's pretty rare I sell drums (I have sold some, just not many). Plus most of mine are modded in some way or have replaced parts and I dread the day I have to sell them and explain every little widened hole and rewrap and unoriginal tension rod. =)
Use the model a friend of mine uses, again with bikes. He has literally dozens, but they are all black, so when he gets a new one and his wife says "Is that a new bike I see in the garage" he simply says "what that old thing, I'v had it for years".
As long as all your kits are the same or similar colours no one will know for sure how many you have. Except you.