Because it is so easy to self-publish, both ebooks and paper books, people leap before they look. The only problem with that is if the work isn't professional level, it won't gain traction.
I casually collect first editions. It is all the better if they are signed. While getting a personalized signature from an author seems the way to go, unless the author and I know each other, I'd just as soon that they don't personalize it to me. But that is my preference. I'm not a serious collector, so I'm free to do it my way.
Nonetheless, as a publisher, I'm less enthused about publishing a second edition than a first edition. Of course, it depends on the circumstance of the first edition, but it does weigh heavily in our decision to move forward on a project.
What is a first edition? It is the first publication of a book. These days, that includes ebooks, though I find ebooks a bit difficult to add to my library of first editions because they fall over on the shelf (kidding), so they don't interest me (true).
Obviously, a first edition is not the first version of a book. They start as a manuscript and hopefully by the time it is submitted in a query, it is not the first draft.
After the ms is under contract, depending on the publisher, a galley copy will be printed; printed, not published. This is an extremely small print run; extremely small. This copy is sent to book reviewers and sometimes to book purchasers for major book retailers. It is a rough copy of the book with the purpose of introducing the work to reviewers who will later help "put the word out" about the book that is timed with the actual publication.
The reason that Cactus Rain rarely prints galley copies is that very few small time reviewers, bloggers, or even book reviewers for hire, understand that this is not the finished product. They may comment on the grammar or some other non-item for a galley copy, whereas professional book reviewers understand that the purpose is to get the basics of the story into their hands. It is like tasting the cookie dough. It isn't a real cookie yet, but a preview of what the cookie will taste like when it is baked.
(If you're interested in collecting galley copies of books, some can be had at used book stores in NY City.)
Fast forward through a lot of dusting and polishing of the manuscript (ms) and designing the cover art, and a proof copy is printed. After revisions or corrections, ta-da! the real book goes into print and that is ... the first edition.
Querying a work that has already been published is a bit like going to the dealership to buy a new car and being shown the used car section. You might find a good car, but it isn't a new car.
Want to know more about first editions? Look here: http://www.biblio.com/book-collecting/basics/what-is-a-first-edition/