This is kind of a crazy suggestion, I'm not even wholely convinced myself its a good one, but it would certainly be interesting.
Basically instead of having the cost of gold for buying new skills increase incrementally until you hit the 1 plat cap, have skill prices be relative to their popularity like other shop keeper items. That is to say everything starts with a base price for skill of maybe 500 gold, as certain skills get purchased more frequently the cost for them increases, as certain skill rarely get purchased there price goes down. There would have to be a cap on this, maybe 2 plat for extremely popular skills, min 100 gold for ones almost never purchased.
Why do this? Well it would give you a unique way to see what the popular builds are, which skills for your class do other players consider the best and the worst. Further it would reward people who try out underused skills with a reduced price and gives a mild penalty to those who just copy everyone else with a slightly increased price. In every game you already start out with a decent set of skills so in the early going when you dont' have much plat you still have access to some good skills, and you can purchase some under used ones if you want or save up for better ones. It would sort of give you something to look forward to, saving up for the more popular skills.