Generally my stance is that if it has gameplay exclusives then fuck that, I'm not even going to get it during the KS.
Maybe not the greatest way to weed out what to buy, but there's enough good looking games coming out that I won't play them all anyways (lets be real; most of us already own enough solid games to keep busy for a few years, no more buying needed!)

In that spirit: Do not give in to FOMO! Especially since it sounds like the KS has ended but the game(s) in question haven't even delivered yet.
Wait until there's some non-preview reviews, maybe see if you can find a copy to play at a boardgame cafe, FLGS, or online (admittedly less likely with purely solo games, but worth checking), and determine how much money you are willing to spend from there.

At that point there will also be a second-hand market from people that simply didn't like the game, rather than just speculators that ordered extra for resale (and thus have to make a profit)