What I've heard from friends who've worked in congressmans' offices is that the staffers will take all incoming communications - phone calls, letters, e-mails - and then divide them up into either "PRO" or "CON" piles for each bill that's up for a vote. They will then provide a report to the congressman, who combines the data of constituent feelings with his own personal beliefs, political compromises he brokers, and information from lobbyists in deciding how to vote. I've heard the rule of thumb is that for each person who writes in, roughly 10 other constituents feel the same way.

So yes, on an individual level, your vote is worthless. However, in the aggregate, constituent feedback counts for a lot, possibly the biggest single input. And so once you accept that you as an individual are insignificant in the grand scheme of themes, you can actually accomplish a lot by minimizing the personal effort you expend on writing your congressperson and instead getting lots of other people to vote the same way you do.

This suggests an interesting hack. Create a really simple mobile app that lets you subscribe to all upcoming legislation on issues you care about. It'd be structured like a news app or RSS reader, where you can flick it open whenever you have a spare moment and read the latest upcoming issues. And then let you easily indicate your position - perhaps swiping right means "Aye" and swiping left means "Nay". A swipe automatically sends a canned form letter to your congressman indicating your support or opposition for the legislation.

Basically, you're leveraging technology to enable direct democracy. Create a direct information line between constituent and congressperson, where the constituents have all the information available to them that congresspeople do, and can vote just as easily.