I continue to believe that the current double wild card system is better than the previous single wild card system (although still not as good as the system I'd like to see). But the confusion that people have about this is pretty obvious in what I've seen a lot of: claims that this season has been evidence in favor of the new system. It isn't!
The big advantage of the two WC system over the old single WC is that it restores meaningful division races. In the 1995-2011 system, there was no significant advantage to winning a division vs. being the WC; now, the division title is far better than one of the WCs.
But that doesn't happen to apply this year. In four divisions, the lead is six games or more; the division winner has it won, and the rest are either out of it or scrambling for a WC. The double WC does not help in those cases. In the AL West, the A's are 3 1/2 games up on the Rangers, who lead the WC chase. Without the second WC, the A's would close to locked into a playoff spot (5 1/2 up over Tampa Bay); with it, they have a pretty serious risk of dropping from division winner to WC.
To finish up the AL...there are currently six teams (not counting the A's) competing for the two WCs, with Texas up two games, the Rays in the second spot, and then the other four within 2 1/2 games. Without a second spot, would the Royals, 4 1/2 behind the Rangers, still be as interested? Sure -- indeed, since each WC slot is worth only half of what the old WC was worth, Royals fans and fans of the other three trailing teams might find the old system just as exciting as the new one right now. Rangers fans are right in the middle -- looking up is more exciting (they could win a division!), but looking down is less so (they hardly have a WC slot wrapped up, but it's far more secure than it would be in the old days).
That's the American League. Over in the Senior Circuit, none of it makes any difference to the teams in the East and West. What about the three contenders in the Central? The new system probably makes September a little less exciting for those teams. Instead of three teams playing for two spots, we have three teams playing for three spots, one of which is much better than the other two. If all three stay close, it's probably a mild net loss. If one breaks away into first, then it's a clear net loss, as the two-team competition for two WC spots will be dull. On the other hand, if the top two separate themselves, then the current system really helps.
(OK, I suppose I should mention: it's not really locked. The Nats have a very slim shot that they wouldn't under the old system; on top of that, the DBacks are done now, but they stayed mildly alive longer because of the increased shot of a WC).
I'll also add: it's hard to tell how things shake out under my system because it would involve some realignment (into four divisions) and a different schedule. If we ignore the schedule, however, what happens is that a few teams drop out of contention, but the Red Sox, Braves, and Dodgers probably have a much more exciting season -- but also are rewarded much better in the postseason for what they did in the regular season. Oh, and there's a much better chance of contenders for the same spot playing against each other in the last few weeks.
In fact, I should probably highlight this, although it's not just about the 2WC system: Despite all the teams in the running, this weekend there's only one series between contenders for the same spot, with the Rangers playing the A's. That's pathetic.
None of this proves anything. All systems have advantages and disadvantages; the fall of the cards in any particular year can turn out any which way. It's just very strange to me that people (and, sorry, I haven't saved any cites, but I've seen multiple examples) would claim that this year is particularly good for the 2WC system.