Here's some generic info
I can give you some generic info about Help From Congressman's Office,
based on my Experience :
1) All of them follow an identical procedure. Thus there really isn't a good
Congressman and a Bad Senator. The only diff may be the person/intern
working at the Constituent Services section. Typically they are
temporary people looking to build a resume for a career jump. You can
imagine, therefore, what kinda service you will get.
2) You can't have 2 Congressman's or Senator's Office pursuing your case
at the same time. I tried Sen Corzine since my Local Congressman's
been dilly-dallying. You can't do that. Only one Congressional Window
can be open with USCIS.
3) USCIS has what's called a Congressional Unit. This is where your
Congressman / Senator touch-bases. My opinion is ..this is a shade better
than USCIS National Customer Service; but not a whole lot better.
Thus they can't move your case. They can't help you with delays etc.
Summary : Try it, doesn't harm; but not of much help.