Joe Biden, a leading contender for VP if you believe the buzz, was the least wealthy member of the last Senate and is likely near the bottom in this Senate.
Now, there is nothing inherently ennobling about being poor (I'd be a better man if there were), and there is nothing inherently corrupting about being rich. But the fact that Biden has been in the Senate for 35 years and hasn't seen his personal fortune blossom means that he hasn't used his position, and all the connections and insider knowledge that come with it, as a cash register. It's an easy thing to do without ever overstepping legal boundaries.
Biden has chosen not to. I think that speaks to his priorities and why, fundamentally, he is in Washington.