Here's my idea for making Skillchains more useful (and perhaps giving a reason for certain jobs that might not normally SC to get involved) - stat bonuses for SCs to those who are part of the SC. Now I know that sounds like it could get overpowered, but let me explain. Let's say you have a SAM and a THF working together since this is a combination I've used time and again in my very long FFXI life.

1) SAM uses Tachi: Enpi > THF uses Gust Slash (just an example, don't go ripping into the weak SC). This causes a Detonation skill chain to occur and, for say, 30 seconds, the SAM and THF gain a bonus to AGI. If the THF closes with Dancing Edge instead, this causes Distortion and both would receive a bonus to MND and INT. Doing Tachi: Kasha > Shark Bite would cause a Light SC and both would gain bonuses to STR, DEX, AGI, and CHR.

2) The bonus would scale upward with job levels, day of the week, weather, and TP. For job levels, the bonus would be stat +1 at Lv. 1-10, +2 at Lv.11-20, and so on. For Day of the week, if the day of the week aligns with your SC, the duration of the effect increases by 50% (so 45 seconds). For weather, it increases by 50% (combined with day it would mean the duration would be 60 seconds). For TP, for every 1% over 100% TP, the duration increases by 1%. So effectively, if you did a SC at 300% TP, the duration of the effect would be 1 minute and 30 seconds.

Now I know you're looking at that and thinking "couldn't that be abused big time?" You're right, it could be (especially by SAM mains and /SAMs) if there wasn't this catch - doing a new SC with an old effect still in place, will not overwrite the old effect, nor will the effects be accumulative. In other words, the best you could ever hope for the duration of an effect, assuming the right day, double weather, and 300% TP, would be 2 minutes and 15 seconds (all % increases based off the original 30 seconds).

3) SC off of a SC will cause the stat bonus to go up by +1 for a secondary Lv1 SC (Transfixion, Detonation, etc.), +2 for Lv2 (Distoration, Fragmentation, etc.) and +3 for a Lv3 SC (Light or Darkness). This effect IS cumulative, but once the duration of the initial effect is over, it all goes away.

I hope I've clarified this enough, but that's my idea for making SCs more appealing. Any questions on clarification, feel free to ask.