But they don't! If you plant a number of different seeds at the same time they won't all mature at the same time.

I agree about changing prices in the nursery, and can't see much to add what you've already said about the "bargaining algorithm". I'll often shut the game off, or switch to VV or some other task on the computer while the plants are maturing. Perhaps I'm willing to take more risks than you, or you're a keener bughunter.