I think that the concept is still way too early to make any judgements about its likelhood or even possibility.
if you look at the universe you do see sign after sign of replication. We see stars that are similar, galaxies that are similar, movement that is similar and an underlying basic set of rules that seem to define motion and form.
Given that, I would not be surprised to see things replicated at lesser levels as well. That does not imply that life, as we see it would be the same, I would expect to see similar diversity no matter where life was found. But I would not be surprised to find that the basic building blocks were not uncommon throughout the Universe.
edited to change common to uncommon in the last sentence.
Earth is the only example that we have studied. Anything else can only be in the realm of pure speculation for some time. Once we have more than one example of life, preferably once we have several examples of life, then things like panspermia become a better topic for research.
Right now it can be nothing more than speculation.
Considering the time spans required for distribution of starter material through pansperpmia would be similar to the times needed to do the same initial work through natural processes, I don't see it being likely. I would imagine that it is just as likely that any starter system delivered between habital worlds wouold find the ecological niche already filled. It would then depend on which starter body competed best to fill the niche.Aslan is not a Tame Lion