> Smaller stars last longer, but they also emit less energy and so there is less likely to be higher life forms just because there isn't enough energy to support life.

This isn’t really true. The energy density at a planet’s surface is a function of both the star’s luminosity and the planet’s distance. Most star’s (at least in the Milky Way) are small, and most stars have planets in orbits closer than is Earth’s. The so called “Goldilocks zone” is expected to have at least one planet in it for a very large number of stars (again, at least in our galaxy).