I think this sort of abstraction is only worth the extra development time if you need to support different database formats within the same application. If we were ever to try to move away from MySQL, we would probably want to look into this.

That said, I have been doing some work recently to make sure our SQL statements are packaged in subroutines. There are some places in the legacy LJ stuff where it's embedded directly into BML files, and that makes me cringe.