I don't think the "I'll pay anything" guys make valid points. Most people do not judge the reasonability of a price on the amount of work that is put into a product. (Nor should they.)
When one purchases something, they ought to evaluate the value of a product solely on the utility that they gain from that product and how that compares to the utility and price of similar products. Tweetbot is working against the precedent set by other apps in this regard. It yields near-negligible utility over free alternatives and competes in an ecosystem dominated by free apps. (If anything, it yields less utility over others, because once the token threshold is met, it will in all likelihood become abandon-ware.) Thus the value of Tweetbot— and of software in general— goes down.
The work put in by the developers has no weight in determining the price. The market's tolerance, perception of value, and willingness to pay is the only factor. Even if I spend 10,000 hours making a great latte, it's unreasonable that I charge $1m for it because my competitors are selling a similar product at $4 and the increase in utility of my latte versus theirs is likely not enough to warrant the increase in cost to the consumer. Their logic is flawed and is totally incongruous with the most fundamental concepts of economics. Commerce is a quid pro quo, not a charitable donation.
I don't, however, believe that such a high price is a knock against TapBots. They are permitted to charge whatever they like. You really can't fault them for price-gouging: Everyone loves money. The desire to get more of it is something that is not only reasonable, but is lauded in a capitalist economy. I find it doubtful that many people think ill of TapBots for their pricing. Rather, the issue lies in the fact that their app does relatively little yet has an incredibly inflated and anomalous price that deviates from the norm. The motives are reasonable, but the price isn't.
As for me, I won't be buying TweetBot. It's more money than I can reasonably afford. Even if it weren't, it's price simply outpaces it's value to such an extent as to be unjustifiable.