Yeah, there can be a bit of that, and it more often happens on topics that have been done to death like multiplayer or UI or bodily waste etc. When I link posts it's never in a "Learn to search, noob" fashion because I know that most of the time they are only easily found if you already know about them. One of the threads I linked was ultimately locked by Threetoe, I recommend reading that one for some fun if you only skimmed it (I think it was the one that had a wall of text OP). That one started getting fiery.
More on topic, I think the thing about paying for stuff to go into DF is, everything is going to go in anyway. And if there's something Toady doesn't want to add, attempting to pay him for it won't change his mind (that could be called assumption on my part but I'd say it's at least educated assumption). So what you are left with is paying for priority, or what you think should go in first.
And Toady has shown that he prefers to work at his own pace and on what he believes should be next worked on, either because it makes contextual sense to work on it at the time, or he needs a break to work on something different. Currently he's getting enough money via donations to live and work on DF at the same time so there's little reason for him to willingly adopt a payment model that would make him work in a way he'd rather not.
So what you'd need to do to have your idea implemented is to convince the donators to stop so that Toady's income stream would dry up so that he'd be more amenable to a bounty style system on adding features and content. Keep in mind that I think Toady mentioned that he's not against returning to work in some fashion if he had to rather than bend over backwards for money to support development.
Personally, I think the way it works now is fine and don't think that what you suggest would work well. Consider the game that has already been made and is still actively being worked on, consider what is in current development, and consider the current funding model that keeps Toady independent and answerable to no-one. Why would you try to fix something that isn't broken?
The answer for us of course, is to get something we want put in faster than it otherwise might be. And I can't really argue with that. There are many placeholders and lack of current features that make my OCD rage and keep me from playing properly and I would pay to have them seen to now rather than in x number of years, but they're probably nothing that you or most of the other people playing care about. So I simply wait patiently and reward Toady generously when I wish.
The answer for Toady is of course to get more money if he wants, but he's happy with how it curently is and has declined to follow any number or marketing/money-making ideas that could easily net him piles of cash. It's pretty remarkable actually.