I know we're all dissapointed with group SP bonuses. I feel the same way. However, I would like to take a little time to talk about Behest, as I have found that it is a VERY viable way to gain SP, at least up to r28 (where I'm at now).
I spent the afternoon doing leves, and stuff around the house. But I would always come back and try to be around for Behest, because I wanted to see how it worked. Well, the results were pretty fantastic.
I focused on the r30 Behests, but I believe the SP should be pretty good anywhere. The best thing about Behests is that you CAN do them solo if no one is around, or if there are a LOT of people, you can all group up and still recieve excellent SP rewards. I'll break down a few of my Behests just so you can see what I'm talking about:
1. Cedarwood: I duo'd this Behest w/ an r18 thm that was just there for healing support. There were 15 mobs that we fought, each one netting us about 100-150sp and taking about 20-30s to kill each. We had no deaths, and by the end of it had gained about 2.5k SP and 6k gil in about 10 mins.
2. Cassiopeia #1: I soloed this Behest. There were 7 elementals that I fought, each one giving me 180-200sp. The "boss" mobs were Efts, and I was quickly massacred so I didn't get to see gil rewards. If Efts pop, DO NOT SOLO THEM! =P Regardless, I still made almost 1.5k sp in about 5-10 mins.
3. Cassiopeia #2: There were 3 of us this time, and 16 elementals + boss mobs. Each elemental netted about 120-140sp, bosses 150+. We beat it in about 5 mins and netted roughly 2.5k sp and 6k gil, along w/ 2 clusters each.
4. Cassiopeia #3: There were 7 of us in the group this time. We fought 31 regular mobs and 2 bosses. The whole behest again took only about 5 mins, and each mob gave 110-120sp and bosses 140. We gained about 4k sp and 6k gil in 5 mins.
Now, I haven't tested this with any larger size group, but so far it seems like the larger the group, the MORE sp you gain in the same timeframe. Kills were happening super fast and it basically felt like a modified merit pt from ffxi. It was a lot of fun, no one died, and we made some good SP off of it.
TL;DR: Behest is not only fun, but very rewarding and larger groups seem to benefit MORE due to more mobs spawning but time to complete remaining roughly the same. Hope this helps people. Happy hunting!