I do something similar, here's my Makefile -- I have scripts that build figures in a separate directory, /figures. I'm sure it could be terser, but it does the job for me.
I noticed that you have some file dependencies not encoded in the targets. Also, you might like reading up on Automatic Variables ($@, $^, $<, etc). Anyway, just for fun I tried rewriting your script in a way that should Just Work a little better.
Check out latexmk: it keeps track of having to run bibtex etc, and runs latex "enough times" so that all equation refs etc have stabilised. (Latexmk -pdf to build a pdf, default is dvi.)