The first book sold very well by the standards of self-published novels (over 1,500 to date and still selling steadily).
Anthony,
I think it might help others more if you gave us some idea of the time frame over which you've sold those 1,500 copies, and gave us some idea of what 'selling steadily' means.
I did the self-publishing thing for a work of non-fiction back in 1993. I used a xerox machine and spiral binding - it cost about $2.50 per copy, postage was about another dollar, and the book retailed for $24.95 per. I cleared, if I remember, $19.90 per sale.
I lived (not too well) off the proceeds for about 18 months.
(The book was advice on organizing a team and competing in paintball tournaments, something I had been doing successfully for the previous decade and had a ready market for as I was regularly published in the various paintball magazines and regularly in attendance at the various tournaments.)
I could have made more per copy if I had gone the route of printing say, 2500 copies up front, but instead I opted to cash the checks/money orders and then walk on over to the print center with my original, run off the day's orders, collate, bind, address the envelopes and then walk to the post office and send them out. (I think the spiral bindings would have gone from $1.20 per to .90 per at that volume.)
The manuscript had originally been submitted to a small press (Mustang), which had previously produced the only other book devoted to paintball tactics. I was prompted to write mine as a response to that other book (very out-dated and, in many respects, very unrealistic). I spoke to the publisher on a number of occassions and, rather than discussing my submission, he kept on trying to sell me boxes and boxes of the previous title. Seems that sales were a bit slim.
Since then the book's gone out of print. (Updating it for today's game would be a new project entirely) I still get occassional requests for copies from 'old-timers'. It also got me a writing gig on the only mainstream 'big NYC publisher' produced book devoted to paintball - The Complete Guide to. Now in its fourth edition.
I have some 'ins' at various publishing firms (both fiction and non-fiction) (a cousin sold his travel book publishing company to one of the big conglomerates and is/was still highly respected over there. The same company owns the 'idiots guide' label), and even those connections, coupled with the previous proven track record can't convince those people to take another paintball book. (The other two I've written are 'How to Cheat at Paintball' - sarcastic, negative AND effective - and The Parent's Guide to Paintball, which is showing a little movement, but...).
As for fiction; I'm shopping a 'in the universe of' anthology series right now (my own writing for the project consists of the author's bible) and, again, old fannish contacts and some author friends are helping me past the slush/query pile (seems many of my old fan friends are now line editors at some of the big imprints), and I have a small press publisher friend who has offered to do the project - but we're all agreed that I ought to pursue the big guys to exhaustion first.
My own fiction is going the traditional route; again, I've been fortunate in having some professional editor friends who were willing to give it a look-see and have said 'its saleable' (about the only measure that counts), so one short will soon be off to the magazines and a novel will soon be off to a publisher. The only possible exception is a 'for-fun' project (sf & paintball) that's out there for the paintball community to read as I write it (there's a large contingent of sf/f readers/watchers amongst paintballers) and, if its sufficiently well-received, I might go back to my small press friend and see what we could do with it.
So, that's my personal experience with traditional vs SP. Use self-publishing when the market and product are a match and IF the current circumstances suggest that its a profitable match. Otherwise, go the traditional route, as its a lot easier to sit and write and get a check than it is to sit and write and copy edit and proofread and print and collate and mail and promote.