You really don't want us to play more than one char, do you? Normally in games when they put out a new class, there are events specifically geared to help you level that char up,Blade and Soul Gold and rewards for doing so. Here, story, and side quests are the big source of XP for leveling chars, but the XP event is for kills, and dailies, which favours level 50+ chars that have finished the story, and side quests. The other event is also squarely aimed at level 50+ chars doing the daily challenge.
You'd make so much more from your non-whale players that would buy costumes, and other things for their alts if the game wasn't so alt unfriendly. Here are some suggestions:
-Have all chars on your account automatically added to your friends list, and have mailing between them free, or just add a shared account storage tab. Account storage would even give you the chance to sell more storage expansion items.
-Make items used to upgrade equipment Buy Blade and Soul Gold (evolution weapons, powder, XP gems, materials, etc...) account bound, not character bound, and without requiring a cash shop item to send them like costumes do, it could cost gold, as a new gold sink, but not real money.
-Have market restrictions applied to each character, not your account.
-Let us move skills to different hotkeys, as different classes, have equivalent skills, but under different hotkeys (ex: ones that knock dazed/stunned targets into the air) which makes playing multiple classes harder than it should be, as we're effectively fighting the UI, and learned habits.