That's a pretty interesting idea. I think that making it bi-transactionable would be a good move, but the core problem still remains. SP points become nearly worthless (like gold) after so long of playing. While your idea would see benefit, I feel it would be best to tackle the problem at the source and "do it right" if anything is done at all. I've come up with some interesting ideas for a replacement, such as a tiered system of skills. Each sublevel of a skill would be adjustable and each parent skill would impact its subskills in addition to the subskill itself. Also, getting away from an awarding of SP for each level seems like a good move. Skill points might be best if they were dynamic based on your actions in the server only. This would serve two purposes:
1) Skills would be more reactive to what a player actually does. You couldn't instantly master a skill in five minutes by clicking a button with thousands of saved up SP. You'd learn your skills naturally based on how you play the game.
2) This would also eliminate the need for pre-selected classes altogether. How strongly you use a skill would cause it to increase more rapidly and also impact how quickly you can learn the other skills--for example if you cast a lot of offensive spells, perhaps that would have a negative impact on physical weapon proficiency. If you quit casting and focused on physical weapons, you could still increase it and eventually increase quickly, causing a negative impact on increasing casting. You would dynamically develop your character as you see fit to play, instead of locking yourself into a fixed set of multipliers. Really. If you were an unskilled person back in the timeframe this is set, you could go and start learning anything with equal weight. You wouldn't start off sucking at swords just because you sign a paper saying you want to be a mage. You simply wouldn't develop the skill as much since you'd be primarily casting. It would be this more realistic (but still gameplay friendly) approach realized in the game. Much more would players be free to build a character that they really want instead of a few classes that may not capture the essence of how their optimal game would be played. This would also prevent the SP buildup problem where people could max all their skills due to sheer saving power. Fun stuff. More freedom. I like pie.
Anyway, that's my current idea.
