I use Frontier Outposts to allow me to capture territory that contains colonizeable territory early, and then leapfrog from there outwards, colonizing and removing the Frontier Outposts as I go.
Unless you are willing to take on an equal amount of "rivalry" Influence, and that would be more than most Etho's are allowed, leaving Frontier Outposts running is a BIG drain on Influence until other means are implemented.
So place Frontier Outpost in colonizable area to secure.
Quickly send out colony ship. Colonize.
Remove Frontier Outpost.
Rinse and repeat and prosper.