1) Nerf leve-linking - removes the heavy slant towards leve only leveling
2) Reduce the Party "Bonus" (Penalty) when playing in rank range - encourages party play outside leve-links by not penalizing so much
3) Let dlvl scale higher than 10 ranks above you - encourages parties to take on more challenging content instead of maximizing efficiency by fighting exactly r10 above you

Current system penalizes you for partying larger than a duo - since a duo can easily handle r10 above them in a fairly efficient manner there is no incentive to party up outside of leves. The incentive only exists with leves because party members can bring leve links. The solution is not to add more leve-linking to the game, but instead reduce the sp bonus for leves, and make partying outside of leves are more viable form of play by letting parties challenge higher ranking mobs and get rewarded for it.

Right now, when I'm in a party and you kill a hard mob that takes a while to kill and you get rewarded by "yay, we killed it" and then you go "oh...they nerfed our SP...I guess we should just grind low rank mobs". Reward players for grouping up and fighting harder mobs. Theoretically I should get the highest SP per hour by getting a good group together, playing well, and destroying really high rank mobs. But no, that is not how we are encouraged to play.