Two types of Kisiis as at Now. Those driven by Anti Luo Dominance in Nyanza and those driven By Anti Dominance by Mt Kenya. Nyachae managed to unify Kisiis in 2002 because he of betrayal by Raila and Moi.
In the 90s majority of them voted for Moi and KANU. Next year they will divide the votes between Ruto and Raila ans depending on how they play the cards UhuRuto played well with Matiangi and Railas blunder in Kajiado they edged out Raila in Nyamira and shared the spoils in Kisii county.
They have strong clan ties; but like you say they are so independent minded, quarrelsome and hard headed to be united. Politically when Nyachae run - they scored 6 percent - so we can say their total political punch is around that- but they certainly punch way above their weight.
Does mogusii vote as a block? I doubt. They are very independent minded one thing I like about them, though they retain strong family ties each has his own thinking.
Kisii vote is largely diluted because of living in diaspora areas that they don't exert their overall influence,diaspora Kisii I would think are different from proper Kisii,all in all Kisii are very policy driven apart from the usual stereotypes.