The Washington Post's Robert Samuelson makes an interesting point about the Enron/Campaign finance connection.

Even if Enron deserved help (it didn't), few politicians would have risked public wrath by rushing to its aid. What this episode actually shows is that the breadth of contributions insulates politicians against "undue" influence by large donors.

This is also the main reason that most people spread their contributions around. You don't want some elected official to totally ignore you because you gave them nothing. Instead, you give them some campaign cash, even if you give their opponent more, at least you have some influence. I'd also rather have a politician that gets a lot of contributions from many different sources, than all of his money from just one source. No one can serve dozens of masters, instead they serve their constitutents.