In "Mastering the Game of Let it Ride" Stanley Ko addresses this topic. Ko says, most of the value in seeing other player’s cards is when you have a borderline hand of 4 to an outside straight with no high cards or JQKA. Viewing a single card should not encourage you to "let it ride" but seeing a card that won’t help you should cause you to "let it ride." Ko doesn’t indicate that this can result in a negative house edge, and I doubt this chips away at the house edge much at all.