Larry Stone has done the work, and figures that an additional Wild Card in each league might have meant four additional postseason appearances for the Mariners (or maybe only one; it's complicated).â†µ
Which is interesting if you're a Mariners fan, probably. For the rest of us, Stone's also listed the second Wild Card for both leagues in every season since 1995. I believe the other big winners would have been the Giants. But you can see for yourself.