Term limits would solve the problem of campaign finance. Lobbyists and special interests "invest" in a candidate with the assumption they get YEARS of influence. So the incumbents get re-elected.
The challengers do not get the financing to mount a challenge.
Even with campaign finance reform, incumbents would continue to have the edge just by utilizing constituent services in their offices, use of the media, public laudatory comments from other incumbents of their parties, media appearances garnered from their public office position etc.
Term limits would really level the playing field.