Actually, the Factotum's spell access is per-day. Inspiration is per-encounter, but the spellcasting is per-day.
I freely admit that I misread the ability. In that case, the spell access is less powerful but only slightly; you still gain access to 7th level and below spells from the Wizard/Sorcerer list; even if you only get 8. Spell Turning, Limited Wish, and Contingency are all looking mighty fine. So is Alter Self, Polymorph, Planar Binding, Antimagic Field, True Seeing, and Major Creation. Greater Teleport and Teleport.
So you get two high level spells per encounter, basically. Hm.
I'm still skeptical, but less so. The spells rogue is showing more endurance, but the Factotum is showing burst potential and downtime potential.
Edit: Also, factotums have greater access to the Frank trick, which is a big deal in adventuring.