I think you have more space than me Gavin.
My collection is stacked fairly well but as those that have visited me will know, the space is tiny. The collection doesn't spill into the house and there are just one or two items in the lower floor of the garage.
I always had a list of models I wanted. These were ones that I considered to have cultural/historical currency or had a personal nostalgic factor (within a realistic price range). These I was prepared to pay for. I have amassed others beyond that list because I've got them for free. I've also made it an aim to collect original manuals and some software for those models. Nearly all items have now been ticked off that list and my focus has moved from collecting to mostly minor restoration and maintenance (and videoing the machines).
I make it a priority to have the computers working. Spares are useful for this, but they do take up more room than I'd like, unless they are just a circuit board. Consequently I don't have many duplicates, but I'm confident that if something does break down I can get a replacement IC or maybe a whole mainboard from somewhere.
However I find I've got some old cases (carcasses), books, replaced tubes, parts of models I don't even have (and don't intend to get) and some non-notable computers which really, I could probably do without. This is the flotsam and jetsam of which I speak...