Except you CAN'T take money out. Are you saying that I, a private individual, can't express my political opinions? Well that's the entire point of the 1A.
But term limits does a few things. It reduces incentive for large investments, because you won't get your moneys worth, it reduces incentive to take said money, because you can't use it (if you can't get reelected, why buy ad time?), and it allows actual reform to take place. Because as it is now, the people that are supposed to reform the system are the ones benefit the most for it remaining the same. Right now you CAN'T elect reformers because of seniority. Even if we, as a nation, were somehow able to elect 33 new senators all hell bent on ending corruption, they wouldn't be able to. They'd need to sit a few terms to gain seniority, and then MAYBE they'd get a shot at being on a bullshit committee, and THEN maybe after a couple more terms (provided they play along of course), they'd get a chance to be on an important committee.
Term limits would completely change that dynamic.