I have not seen any overpriced assets. If I charged what it costed me in time to make my assets, I would be charging at least 100x as much.
Woah necromancy at work
I see this argument a lot about a AAA game costs $60 so why would they pay $40(?) for only one part of what they need to make their game.
Just because a game costs $60 to buy has no relevance to what you are buying on the marketplace.
Game companies often spend over $10-$50 Million on just coming out with another sequel each year. Most of this money is spent on labour.
Anyone who thinks paying $40 for an asset to help you build your game means it should provide you a game ready to ship or to be steam green lit because you can buy a AAA game for $60 is crazy.
If you think the prices are too high people can always spend months/years learning how to do something professionally and do it yourself. 
Yep… it’s non exclusive. But this is even true for the free stuff on the market place. So you would recommend a higher price to decrease the number of potential games to 500 and ignore the free stuff? If you would get exclusive stuff then the solution is more money and not less. I would not buy my main-character like a “Super Mario” from the market place but does it really matter that much if a brick looks like the same brick in another game? I would not make my brick pink with green dots just to be different anyway. So I don’t care if other uses the same bricks to build some house if I could save a lot of time. Does it matter if a bush looks like a bush somewhere else or a …rock? Or a background mountain …or dunno an AK-47? This is not how I would differ my game from other games. If somebody thinks: Oh no …not again THIS background mountain then I did something wrong with my (too boring) game anyway? I like the marketplace. You could save a lot of time if you use it right… even if it’s non-exclusive.
The prices are no issue to me, but when they say in their description that they are adding more features eg:(main characters) then the price is an issue as you are paying more for that support and you are stuck, this has happened to me, and I think the people in charge of the marketplace should be looking at this.