i hate skill decrease, that would mean that after a while you cannot gain any more points for a skill since if you start training, another skill would become less, and you would have to put all your time into keeping your skills.
i do hope that your skillpoints will be like 10-20 per lvl at start (depends on how high your lvl is) since each \"updrade\" will cost more. if it is just 1 skillpoint per lvl, you need at least 3 lvl for a new skill. or you would have to gain lvl fast, like 1 per 2-3 monsters.