-Increase the Incubi Strength by +1 (so S5 base, S6 with Furious Charge)
-Increase Incubi WS/I by +1 (so WS6 and I6, putting them on par with elite enemy characters)
-Increase Incubi armor by +1 (2+ save means they become like uber Honor Guard)
-Grant Incubi Fearless
-Add +3″ to their run moves (with natural Fleet, than means very solid ability to foot slog)
-Grant the squad in essence a “Psychic Heavy Flamer” (to soften up hordes)
-Give the Squad Shrouded (combined with some terrain and they are shrugging off even AP2/3 shooting).
As you can see, the Spirit Seer potentially brings A LOT of utility to an Incubi squad. If you really want to go crazy, add a Spirit Seer and Jain Zarr to a squad of 8 Incubi in a Raider (Jain Zarr’s Mask decreases enemy I and WS by -5, meaning that the lack of grenades doesn’t matter so much and also increasing the sqauds’ damage and survivability in close combat; oh, and she is a beatstick herself in the assault phase). Pretty much anything they charge should be toast and, with the right psychic abilities and Power through Pain buffs, they should become pretty survivable as well.