Some of the stuff I'm about to say has probably been said, but I'm giving my 2 cents anyway.

I think these ideas should be implemented only after there has been more PvE content added to the game.

Make leves solo only, don't change SP/EXP boost rate, reduce the leve counter to 24 hrs. With this change leves become like daily quests, something for the casuals to do for an hour or two then log out. With this change people would have to go out and party get increased rates of SP/EXP.

The current party/battle system just needs to be tweaked a little. Some monsters need to give more EXP/SP for their difficulty and for others, less.

For the casuals that want to party but don't want to grind, there will still be behests. It would have the leve-like SP/EXP rate boost and the party SP/EXP boost and each camp would have level requirements. Behests would happen every 30 mins, but you can only do it once every two hours. This is to keep people from abusing it since behests would give you a party SP/EXP boost and a leve-like boost, which means a lot of points! Having the behest every 30 mins gives the casuals a chance to join a behest whenever they log in and gives others multiple chances to get into a behest since parties will be limited to 8 members.