Only quoted parts I felt were relevant, not really looking to dive into another opinion war.

I disagree. The clamour for cheaper products leads the companies to
produce said product.
If you want to look at it that way be my guest, but the reality is competition does far more to reduce prices than consumer noise.
No, consumers want products for fair prices, there’s a difference. In
case of DLC, that price is subjective.
No consumers want for nothing, always have and always will. Would you rather have something for free? Of course you would. A $1 for WK instead of $7? Hell yeah you'd want that. What consumers want (Everyone wants for a little as possible) and what consumers view as reasonable (Incredibly subjective to every individual) are two completely different subjects.
You do have a choice.
You either abstain from your two beers, or you don’t buy it.
Simple.
If enough people don’t buy it, EA will either lower the cost, or stop
making DLC.
Or, I could say

you to the beer charging $8 and pick up the beer being charged for $5. If I don't want to pay $5 for RTO, well I'm out of luck. So no, you don't have the same level of choice. This is what I mean when I say no choice, EA has you by the balls and can price as they please because there is no alternative for you. Obviously they'll keep it at a level that will generate their target number but you aren't getting the price you may be getting if their was a second party.
But you can’t complain about pricing without knowing what you’re aiming
for. Like you said, value is subjective. The question is, how much will you
pay to entertain yourself for two hours. In my case, the DLC is a no-brainer.
What I'm complaining about is that we don't know if we're getting hosed or not. EA has a monopoly on Dragon Age DLC, they are free to set prices at will so long as they can assure themselves they reach their target. Again, if another company came in and said we could do Warden's Keep and sell it for half the price than it's obvious there is better deals to be had that still lead to financial success for the company. If you're willing to pay the $5 than fine, if it's something I feel than I'd buy it to. The gist of my posts isn't that DLC is overprices, rather that it's set up to easily exploit us consumers.
Do you really believe that if sales of DLC are really bad because the
majority of people aren’t buying the product due to price, that this won’t, a.,
kill the product, or b., drive down the price?
Honestly I'm not sure a DLC will ever truly flop due to pricing alone. Again people who want to expand their game have no other options will pay what is asked of them, I think The Sims 3 has proved that notion very well. If people are willing to pay for it than their willing to pay for it, I'm not arguing against that.
Is there any evidence to support this?
At the end of the day, if it’s not in the favour of the consumer, it
will fail.
Basic economics, the less competition in a market the less tilted that market is in favor of the consumer base. EA holds a monopoly in DLC for BioWare products, so they completely control the market and pricing for said products. And a market does not need to be tilted in favor of the consumer to succeed, to succeed all it needs to do is put out a desirable product at a price people are willing to pay, if people are willing to vastly overpay than it's even better.
Right. But if it’s as long and as deep as WK (i.e. dwarf-like and
similar to a baby’s paddling pool), people won’t buy it. Why? Because they’ll
read a review and see that it isn’t considered as value for money (at $20). – I
know that the obvious answer to this is twofold, 1., that value is subjective,
which is true, and that 2., people don’t read reviews. My answer to 2 is that
you can’t legislate for idiots.
Not necessarily, I thought the same thing with The Sims stuff packs but they sold like hot cakes, I wouldn't be surprised if quite a few people would spend $20 on a WK size DLC. Again if enough people are willing to pay that tag and it becomes their peak pricing, what is there to stop them?