It must be made from either quality steel or titanium, these are the materials I trust and prefer in the long run, especially lightweight ones. I don't care about being it race-bred or "posh", if it fits the above requirements, it stays with me for a looooong time, I'm sure.
Well, it seems I found the explanation for the lack of space in the shed :facepalm:
High end means good quality, good function, and designed well enough to still be going strong today. Something like my Brian Rourke frame, or a bonded Dynatech Diablo frame. Deore DX would be another good example.