I used to collect unopened sets. Then suddenly one day I decided I was running out of room, and the reason I was collecting them, was just that, to collect them, not to re-sell them. So I made the decision to open them all, and store them in individual ZipLoc bags. I folded down the boxes nicely and I save those too. By doing this it opened up the opportunity to build them and review them, which proved to be successful for me. I from time to time go dig out a set and build it, but it only stays built for a few weeks, then it goes back into storage. I am very particular about my LEGO, and this has worked for me so far.
Here is the last picture I have of my sealed sets, I have probably more than tripled this amount by now, plus a grand worth of collectible mini figs
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