Wha'? A two-game series? Erm...don't know how to tell you this, Nico, but...um...two is an even number. I know. And the wild card game should, for many reasons at once, be a two-game series. Here's how I think it should work, and why...
To advance to the ALDS, the 2nd wild card team should have to beat the 1st wild card team twice. That "two chances to win one" backdrop gives the 1st wild card team a significant advantage over the 2nd wild card team. This is important because the difference in record between the 1st and 2nd wild card teams can be large, potentially even larger than the spread between a division winner and a 2nd place team.
Never has this been more evident than in 2014, where the Los Angeles Angels (of Anaheim, if you didn't know) are currently in the 1st wild card slot despite currently being on pace to win 97 games. Leading the 2nd wild card race, at the moment, are the Toronto Blue Jays, currently on pace to win all of 86 games.
A team 11 games worse should not be on such equal footing as to have only to snatch one game, albeit an away game, in order to advance. Consider a team like the Seattle Mariners, also in the thick of the wild card hunt just 2 games back of Toronto, that is on pace to win only 83 games but has King Felix Hernandez as a tremendous "one-game wild card" weapon.
In order to create sufficient incentive to win the 1st wild card, and not just "any wild card," making the 2nd wild card sweep a two-game series in order to advance is more fair to the 1st wild card winner.
The wild card, as currently constituted, also is not advantageous enough to the division winner who boasts the league's best record. In theory, the division winner with the league's best record has the benefit of playing the weakest playoff team in the ALDS. This, however, incorrectly assumes that the wild card teams will be worse than the division winners and this is simply not always the case.
In the AL this season, if the 1st wild card team advances then the team with the best record in the American League, and in all of MLB, will play the team with the 2nd best record in all of MLB. How does a two-game wild card series help to recalibrate the level of advantage?
If the 1st wild card team (currently the Angels) wins "wild card game 1" then the team with the AL's best record (currently the A's) have the advantage of both home field advantage and the Angels having burned their #1 SP in the wild card game. However, if the Angels win the wild card by losing game 1 but winning game 2, they have burned their #1 and #2 SP in order to advance. And of course if the 2nd wild card team (currently the Blue Jays) are to advance they will necessarily have to burn their #1 and #2 SP in the process.
Suddenly, the advantage of securing the 2nd wild card, the advantage of securing the division, the advantage of securing best record, are all heightened -- yet the 2nd wild card still has a shot at advancing, and the 1st wild card still has a shot at advancing with just one wild card game, and so the balance of power has not shifted to the point where the division winners are sitting too pretty. There's just a bit more separation, creating more urgency to secure the best spot you can.
The Mariners should not have a chance to win 86 or so games, grab the 2nd wild card, and have a shot to eliminate the Angels/A's, having won 10-11 more games, in a one-game showdown behind Felix Hernandez. The same goes for the Kansas City Royals and James Shields. Can you imagine winning 97 games and besting the 2nd wild card team by 11 games, yet having to put all your hopes for advancing into a one-game showdown against the knuckleball of R.A. Dickey?
And the prize for winning the AL West this year, complete with the best record in all of baseball, should include the chance to begin the ALDS against the other team's #3 SP -- or the certainly, if that team is only the league's 2nd wild card.
As long as the system is set up to where a wild card team can have a better record than a division winner, and in fact a much better record, I think measures are needed to maintain the structural advantage of achieving each "higher seed" (2nd wild card, 1st wild card, division winner, league's best record). A two-game wild card series accomplishes this in ways that also add some interesting variables for the ALDS rotations. All for one extra day and possibly one extra game.