Some of that year over year regression is the counter to Jay - some of them had performances that were a little unlucky and we should expect somewhat of a bounceback from at least 1-2 of them.
You also left out Yadi and Shelby as ones who regressed. Plus Craig was worse than 2013 (although he's not coming back).
I suspect, on their own, the Cards likely hit a few more HR next year (Carp, Adams, and Molina will likely hit more, Peralta less, and the RF spot will hit more from Grichuk/Taveras). Absent a transaction, this team is likely to still be below NL average in HR, though.
It's hard to see the Cards signing OF power just from the perspective that they have enough good young OF that they're unlikely to dedicate a bunch of money to a long term signing at that position. If you're running the Cardinals, you already have Holliday, Jay, Taveras, Grichuk, Bourjos, and Pisciotty. If you're going to spend money at that position, it may be more likely to involve a trade of an asset than through FA.
2015 outfield FA are also rough - Nelson Cruz is sort of an OF, I guess. Beyond that? Morse? Rasmus? Chris Young? There's not that much power out there. Cruz is likely the only guy projected to hit even 25 HR from that group. Not enough to spend a bunch of money on in a contract of more than a year or so.
I think the idea of an OF trade is intriguing to me to a certain extent, because we have more bodies than we really need, and there is value in certainty as a playoff caliber team. And, they are the real power problem - our IF is producing league average pop overall.