Quantity vs. Quality in Book Publishing

Interesting observation:  My first book came out in 2011 and then I didn't do anything until a year later.  Once that book came out, suddenly my first book (which had sold next to nothing up to that point) was showing some movement on the sales charts.  This is a good thing, right?

Well, now enter the third book.  With that release my other two books were getting a little more movement and when I did the free weekend on Amazon, my second book was back up on the best seller list!  It was crazy!  

So here's my question:  Do authors who put out MORE books do better just because they have more books out there?  Are people reading their books because they are all good or are they buying them because they enjoyed one and are hoping that lighting strikes twice?

I became friends with an indie author whose work I enjoy.  She puts new books out VERY frequently and her books are all over the best seller lists.  I'll be honest, I LOVED the first three that I read and have been increasingly frustrated with her work ever since.  It's not that she's a bad writer; her work is good, but just not all of it.  I feel like some of it is just...so...long.  Two of them were just painful to read because the story just dragged on and on and on and really, each book could have been about 100 pages less.  Plus, the quality of her work wasn't quite up to what it was in those first three books.  I didn't feel so attached to the characters and some of it felt very...amateurish. 

And yet she's on the best seller list.

When I was working with Susan Mallery, she was putting her books out in three's - a trilogy.  One book a month approximately for three months.  They were great, they were popular and they were all over the best seller lists but then, she didn't release anything again for at least six months.  It was brilliant.  

I want to get to the point of brilliance.  I want to get to the point where I can get people to volunteer to help me out with marketing just because they love my work.  But I guess I have to build up my library of work before I can make that happen.  So for now I am going to go with the quantity factor and see how that works for me.  

I still hope that my work come off as quality but we're going to see how flooding the market approach works.