With most collectibles, condition is a spectrum and a worn example is simply worth less. Vintage board games are crueller than that, because they have a hidden pass/fail test the box does not reveal: completeness. A beautiful old game missing a handful of pieces is not a slightly-less-valuable game. It is, for a player, not a game at all — and that binary nature should dominate how you buy.
Why missing pieces are different from wear
A scuffed box, a worn board, foxed cards — these are cosmetic, and a player can live with them. A missing pawn, a lost card from a deck where every card matters, an absent rules sheet, a die short of the set — these can render the game unplayable, and they are often impossible to replace exactly because the components were specific to that edition. The game's value as a game collapses to near zero, no matter how pretty the rest looks, because you cannot actually play it.
The reproduction grey area
You can sometimes complete a game with reproduction pieces, and for a player that is a fine fix — it makes the game playable again. But know what you are buying: a completed-with-repros game is a player's copy, not an original, and should be priced and described as such. The trap is paying original-complete money for a game quietly completed with modern parts. Ask not just "is it complete?" but "is it complete with original pieces?"
The takeaway
Before you fall for the artwork, count the pieces. In vintage board games, completeness is not one factor among many — it is close to the whole question, because it is the line between a game and a decorated box. Verify it specifically, in detail, every time, and you will never overpay for a beautiful thing you cannot play.