I think it depends on your reason for collecting.

If you are collecting them for yourself, then buy whatever appeals to you.

If you are trying to guess what will be worth something later on and buying for resale in a few years, then good luck, your guess is as good as mine.

I speculate that the market for OOP kits that are being made today will be small. Everybody sees what the old kits are bringing so they are saving a few for the same purpose.

The reason the old kits sell for so much now is that none of us had any idea that they would be worth anything so we built them and flew them and didn't save them.

That said, I would pick up the limited production kits, if possible. When someone makes a run of 50 - 100 kits, or less, then there is only a small number available and at least some of them will get built (like mine).