I don't really see a problem with it. However asking those of us in the collecting circle is kind pointless since we all pretty much do it and will affirm each others actions for the most part. I'm just throwing that out there. I'm not trying to start anything.
I also collect multiples of systems, albeit a little differently. My big thing is hardware or cosmetic design differences. I don't go for limited edition branded consoles. I don't own a Modern Warfare 2 or Halo 3 Xbox 360 with my Arcade that I currently use, but I don't see the problem owning my Arcade, a Slim, and an E model.
My big thing is how do they differ outside and inside. What is their setup? How do they differ during disassemble? What can I learn when it comes time for a unit to fail? I'm actually actively looking for the alternate 360's and PS3's at the moment. System function is optional. Especially when I first get them I'll grab my tool kit and dive in.
I do own many duplicates of some systems. I'm working on getting them fixed up and out though. Come to think of it I don't even know why they are listed in my collection here. Time for some clean up.
Wow that's one heck of a tangent. Sorry about that.