I like to respond with my thoughts. And anything that makes me think makes me happy, so respond I shall.
#1: "Look Outside the Box only after looking inside it". I understand wanting to maintain consistency and all that, but I really think that's a developmental concern more than a design concern. They do tie together, but I'm of a mind that design is far more about being "new and different" than the same-old same-old.
I do have to concede that there's no reason to change something for the sake of changing it; that's why it's important to present yourself with as many different design directions as possible. One of the great things about Magic is that it normally is fresh and new, but when constantly retreading old ground it turns out bad.
I do think Shards suffers a bit from "doing it to do it". While I really like a card like
Kederekt Creeper 
, I find myself constantly looking at it saying "So, why is it blue? It looks red/black." The best answer I can come up with is "it's a common Grixis creature that establishes the color theme of the set" (I don't think a 2/3 body communicates color unless it's distinct. A 4/1 red-white creature with Vigilance would be distinctly red in body; 2/3 in black doesn't seem out of line to me).
Also, just because you explore a design space during the design process does not mean that you have to use it. It is entirely possible that a good design can be cut from a set for reasons unrelated to its potential (I understand a local enchantment mechanic was cut from Tempest because the Licids already filled that space). I firmly believe some days people are more creative than others, and creating a backlog of good designs helps overcome times of "designer's block".
In short, I think the simplest solution to a problem is usually the best; to have the freedom to be creative, you need more new interesting problems.
#2: "If you can do without it, do so". Can't argue with that; it cuts down on necessary complexity. The important thing is to be sure you don't throw out things that are important, but you already addressed that in the article.
#3: "If it doesn't fit, don't force it". I follow this rule already, and it's mostly good. I don't think an ill fitting card is a bad card though; I think it's a good card in the wrong place. I think of it like a good kid with no friends; you don't hate it, you just want to put it in a place where it can be at it's best, and not where it will be all alone and miserable.
#4: "Everything Affects Everything". It's true. I think one of the reasons colors are important is to help group things that are similar where they will play nice with others, while keeping things divided so that you aren't forced into anything. For example, the big creatures in green tend to make you want to play acceleration, which in turn affects everything else in the color green (and the rest of the game). The end result is that players used to play green to get every other color online faster -- the creature color had inefficient creatures because it already had raw power to get them out sooner. Black suffered from a similar problem where nothing that practically won the game on turn 1 could be printed at 3 mana or less.
I think this fits in with point #3 too.
#5: "Pay attention to Feedback". Well, I'll give you some feedback. I constantly feel like I'm on the verge of getting a deck with a new theme together with the sets lately. I don't have many people to trade with, and don't buy a lot to trade, but I still want to have fun with the new mechanics. The other cards are either in a later set, by which time I may have lost interest, or they're at rare where I'll never see them.
When I see a rare that would fit well into a deck I already have, I think "I know I'd like that, it's perfect!". When I don't quite have a deck together, and it looks like I need a rare to pull it together, I think "I don't even know if I'd like to play with that" and tend to buy less (I had this experience when making a mono-black Goblin deck, and realized that to get enough 2 drops I needed four
Weirding Shaman 
s).
I've also had the experience that I can't really put a deck together until the next set releases. I think this is worse than the "block on block violence" that used to happen, because I have to wait so long to get a cohesive deck together, and then I don't get to play it long (to say nothing about the expense).
I really would like if there were more on-theme commons/uncommons;
Hissing Iguanar 
and a few random uncommons (the Elemental and Drake) was a great start that built into a Jund deck that I then started seeking out more stuff for. Without a "critical mass" of cards I don't get around to building.
I wouldn't think this is a problem except I'm constantly told I have a "large collection". It's big, but it's mostly just random cards from packs, so I end up with a lot of chaff, and no real desire to trade. If I didn't see it, I don't know I want it. I feel like I'm ranting now, so I'll stop.
#6 "Listen to the uninvested". That's mostly true, but only so long as you can trust the uninvested people to give you decent advice. You also have to remember your audience.
Sure, you can ask outside people for advice, and sometimes that works out. But unless they are similar enough to you to understand what's valuable, they just won't get what's really important.
That said, sometimes a fresh perspective helps quite a bit with problem solving. Even "giving it a rest" and coming back to it can give you a fresh new perspective.
#7: "Give yourself time". This is the one I've been hurting on most recently. No commentary necessary.
#8: "Mistakes are educational". Yeah, usually. Sometimes, the whole point of trying something is to "see why it doesn't work". When I've taught new players Magic, they'll sometimes say "I don't want to attack, but I don't know why. Can we see what would happen if I did attack, and then back up?". Knowing you shouldn't do something has some small value, but knowing why you shouldn't do it has far more.
#9: This is probably the inverse of #1. Wait, why are you looking outside the box? Sometimes the fact that something is working, but not "the way you want it to" is motivation enough to look for another answer. You can always return to what worked.
Funny as it seems, this means that an apparent success is sometimes a failure. "When you have time" I do think you should analyze what you're doing and try to figure out if it really works as well as you think it does.
#10: As a guy with an interest in human factors, I totally agree. Figure out what makes people tick and use it to make everything better whenever possible. Admittedly I tend to apply it to the most mundane things in life (I still think that using natural mapping on a stove is awesome), but sometimes the little things that nobody quite notices are the ones that make life really great instead of just not-bad.
Therefore, any way possible, they are going into a deck. It will be interesting to see what lessons I learn from this.