[donh]

Sub-light speed is plenty fast enough to populate the
universe with humans within the time frame of a single
geological epoch. It's easy and practical, if you don't
try to send humans, or other impractical cargo to start
with.

[RightWhale]

That's right. The entire Milky Way is about 100,000 light-years across. It has probably been seeded and reseeded several times [10 assuming spores drift at 0.02% of the speed of light] in the past few billion years.