Photographers end up paying a premium for small improvements in image quality once you get to a certain level. This is always the conundrum. Assuming that the kit lens is your cheapest option, along with a telephoto zoom, is it really worth it to "upgrade." Well, ask the question on the forum and the answer always comes back yes. How much money to spend on the upgrade depends both on how much money you have and how much you value image quality, build of lens, small size, etc.
If you are looking at 30-ishmm lens, you could choose a DA 35 f2.4 (cheap), a DA 35 limited (less cheap), a HD DA 35 limited (even less cheap), a Sigma 35 f1.4, or a FA 31 limited (quite expensive). Each one of these lenses will have reasons that make it worth owning and the differences in rendering between the cheapest option and the most expensive options will be small, but there will be plenty of people who end up buying a FA 31 (even though it is about a thousand dollars new), because they need or want that difference. That isn't wasting money, it is just a personal choice made by a discerning individual.
Buying glass, even expensive glass, gives more satisfaction than buying camera bodies, because you can shoot with it for years, while camera bodies are updated all of the time. There is where the money is wasted if you ask me...