The article is great, and one that really puts thought to word about much of how I go about my own collecting (free word of advice: stay away from the "Let's See Some Cool Stuff" thread if you are really on a budget).
One thing that I found myself nodding in agreement each time was your reactions to each of these figures.
KFC [Citizen] Stack - cool, but not quite "Masterpiece". Even more to the point, "Citizen Stack, to me, felt like a really beautiful and large toy not entirely different from the vein that Generations Metroplex exists in, as opposed to a Masterpiece-style high end collector’s item." Yep, I couldn't agree more. Ultra Magnus is a fond character/toy [to] me, and even if something doesn't "fit" a line, I can find myself wanting it. Citizen Stack is just that.
Warden - Again, your own words were my reaction: "He isn’t for everyone, though, if you need to transform your toys on a regular basis with ease and don’t have any sort of connection to IDW Max, then maybe Warden isn’t for you." A local collector friend (Scotty P!) got one, and while it's a cool thing, it's just not for me. If someone wants a full IDW cast, I can see it. I do not.
MP-10B - It's basically G1 Scourge (from RiD). I've not seen a photo yet that does it justice. It's one of those that's so much nicer in hand.
(My MP-10B Black Convoy unpacking on Christmas day, 2013!)
Rotorstorm - Mainly here, I've just curbed any G1 that's outside of US 1984-1990 mostly. I have a Machine Wars Sandstorm, and I really feel it's the best iteration of the mold, despite the neutered launchers/lack of missiles. Were I able to afford a full run of G1 (US, Japanese, and European), this wouldn't be a discussion for me. It looks great to me in those colors.
Leo Dux - I'm all in on the MMC Feral Rex, and this one is probably the one that I didn't have such a stark reaction to in hand. Other than that sword combined. It's just huge.
I think with my stated reactions to some of these, you can already see some of my preventative measures. I'm reminded of this:
I've seen some collectors that are extremely focused, and the discipline that comes with that is admirable. Conversely, I've seen some collectors that "just buy what looks cool" and while some of those guys tend to function well, others just can't seem to keep control.
We all have our pitfalls, and I feel I've done much better recently, I have my own as well.
More advice: I mentioned the "Cool Stuff" thread, and another one I fall victim to more often than not are the clearance sales. Quite a spell ago, once "cheap" figures came around, I'd find myself picking up things that I'd otherwise pass on. "Cheap" figures have their appeal to someone who is already on a limited budget, too. The pitfall is losing focus of the overall picture by basically not seeing the forest for the trees here.
The antithesis of this article can help as well: just stay away. If you already know your weakness is having these figures in hand, just stay away from them. Even touching a really cool figure can be harmful to your collection focus.
Completionism has its own pitfall built in. I think we can all see that one. Long ago, I gave up the idea that I pretty much had to have anything from the "main line" that Hasbro put out. True completionism would even seek out TakaraTomy's offerings of the same line, often resulting in owning duplicates with little to no difference of any significance anyways.
Completionism can lead to the sealed collector, having to have two of everything at least, where one gets a figure to play with and one to forever leave sealed. Having done this with Alternators/Binaltechs, I experienced first hand this pitfall. Fortunately for me, those lines were very brief and have ended. Expanding that type of collecting would blow my mind, I think, were I to go about everything this way.
There's a lot more, but these are a few that come to my mind. I'm certainly not trying to hijack anything here, but these are my natural reactions to reading over this, as this article cracks the door on much of these, I feel.
Again, excellent read, bud!