To colonize or seed life you don't need to launch huge space vehicles with enough life support to maintain a breeding population, though. You can just launch some kind of self-replicating microbes capable of directing themselves into the forms of life you want to encourage over time. The precise ability to do this would depend on your current state of technology, but we're pretty close to developing full blown synthetic biology and genetic engineering ourselves, so it's hard to imagine they'd need to be more than a few hundred years more advanced than us at most. Microbes can be engineered to be immune to most dangers from space travel as well, similar to tardigrades.

To head off the common rebuttal of "maybe they wouldn't have any interest in it," with more advanced technology smaller and smaller groups of individuals would be capable of instituting such a project, to the point where any high school kid with a synthetic biology kit and some toy rocketry kits could colonize the entire universe (owing to relativistic effects). You'd have to assume their society underwent some kind of massive convergence of social norms away from any individuality such that no few members of their species ever had both the capability and desire.

The entire plan is mostly laid out by: http://www.tedxvienna.at/watch/why-aim-for-the-stars-when-th...