This may be more wordy advice than you wanted, but here's my analysis:
A: Don't pay MSRP. As an investor, unless a set is a surefire bonafide winner, do not pay retail for any non exclusive. You're going to be competing with people who got these sets for 25-50% off. Some exceptions happen when say, a set is gone most everywhere else, already selling for well above MSRP, and you happen to stumble on one. But personally, if you're going to spend MSRP, get an exclusive. There's no reason not to. Less people get/hoard them, less are made, and the value is assured to go up.
Among your sets, I bought Captain Americas at retail ($15) when they were basically disappeared, and sold them that season for 40-$45. The sets one is able to perform this with is very rare. Friends Stables/Vet, Hulk Hellicarrier are other recent examples where lingering sets were profitible while still being found on some shelves. But they are the minority. This usually happens of course in Nov/Dec during Holiday sales season, or right after the holidays when rare sets might still linger.
B: Think longer term. Many of these sets disappeared/retired late 2013. I believe that in general, for proper gains to realized, one must wait at least TWO YEARS (or two Holiday seasons at worst) to really gauge the popularity of these sets. As more and more people get involved in LEGO investing, I think this time frame is ONLY GOING TO GET LONGER. You're competing with people who are happy to make very very small profits, so you have to wait for the supply to dry up before the value increases. So for these sets, I think you'd be looking at this coming holiday season to really gauge. However, as other members have mentioned, because of the refreshes and other factors, it could behoove you to move these Captain Americas, Wolverines, Hulks and Lokis (who've already experienced growth, and future growth could be limited) - and reinvest. The Quinjets, Power Armors, and Doc Ock have not really experienced their growth yet, so I think those I would hold on to unless you are feeling itchy about them.
I am going to use a more extreme recent example: Black Pearl 4184, retired Sep 2012. By Christmas was around $140, which could still be very profitible for those who got it on sale, but by Christmas 2013, it was 220ish, and this Christmas up to $350ish. That of course is a very popular and extreme example.
Let's look at a more random set: LEGO 3661, City Bank Transfer, which was a Target Exclusve MSRP $49.99. It retired in Nov 2012, it was selling for about $65 by Christmas of 2013 which is unimpressive, but was close to $90 by this past Christmas, and now the cheapest on Amazon is $135 and there are only about a dozen people selling the set currently.
C: LEGO Strategy: I am not sure if this is a policy aimed at resellers/counterfeiters, but as others have mentioned, the sets are disappearing and replacement minifigures are coming right out. Captain America Vs. Hydra, Hulk Lab Smash, etc.