Giving a static amount of SP is just silly - no. Bad idea.

However, I would take this a step further by making SP/exp gain relative to your rank, and have it reward you the SP/Exp you would've gotten for any monsters you didn't kill. For example, a few guildleves involve killing # of monsters until you kill your targets. But what people usually do is just kill off everything first, then kill their primary targets to maximize SP/EXP gain. Give incentive to go after the primary targets first by rewarding the player with all the SP/EXP worth they would've missed by killing the primary targets first.