LTspice: How to convert .asc file to netlist?
Under the View menu option there is an entry called "SPICE Netlist" which creates a popup window where you can copy the text you want. You can also go into the File menu option and select New Symbol to create symbols you can associate with the .lib files you create, to provide a pretty image to go along with it. (You do need to match up pins and watch out for grounds.)

There is a very good group that can directly answer all these questions and more at LTspice group on Yahoo groups.

I have also written a schematic parser that can read up the LTspice schematics. I wrote it to generate ASCII schematics automatically from these files. It could be adapted to prepare a net list. But I think the LTspice program itself does enough already. Unless I misunderstood your goals.