Here's a page of speculative fiction I have written about Abiogenesis, Lithopanspermia and the translocation of life by intelligent action. This has been directly inspired by the discussions on this bard about these subjects, and I am grateful for the inspiration.
http://www.orionsarm.com/science/Abiogenesis.html
In this fictional scenario primitive life is relatively uncommon, found only in a few star systems out of every thousand; but in a galaxy of 200 billion stars that means hundreds of millions of life bearing planets.
I have assumed that abiogenesis and lithopanspermia both occur, with abiogenesis being somewhat more common; but additionally I've allowed for the occasional instance of life being transferred by accident or design by exploring civilisations. I have called this process Translocation in the essay.
All based in speculation, I know. But can I relate this to the observed sitation in our part of the galaxy?
If a galaxy-spanning civilisation develops in the future, or has ever existed in the past, then translocation could represent the predominant method of origin of life on any given planet. Translocation would also almost certainly ensure that life is abundant in a galaxy, even if the galaxy was relatively lifeless before. But there is no evidence for translocation on our planet- not a shred of verifiable evidence of alien technology has been found in the fossil or historical record (honestly; I've looked at the case for alien influence and it doesn't hold water).
If there had been a galaxy-spanning civilisation on our world in the past we would almost certainly found something, but that is not the case. So translocation seems somewhat less likely. But that still leaves abiogenesis and lithopanspermia; I suspect they both may be fairly common, but this really is no more than a guess.