What Obama or Hillary says at the speeches are completely irrelevant, that's like when some Trump partner like Cage goes to Russia to give some boring ass speech. The speech is an excuse to pay someone. The corporations won't change anything as a result of that. The speech is a cover for an unrelated paid service.
In the construction industry, they'll inflate contracts by using overly expensive materials or methods. Here Wall Street as an easy way of doing the same: they invite someone over, they give them a ridiculous sum of money in exchange for talking about things WS really doesn't care about and which they could read about for free from random blogs, or some TED Talks, probably from people who are better positioned to speak on such subjects than said politicians and do it because they are experts on the matter.
Obama can turn around and donate the money and all that, sure, and get a fat tax deduction in return too, but the fact is before, while, and after politicians are in office, the mere fact that WS waves "highly remunerated speeches" around in politicians' faces is enough for WS to gain undue influence on politics, period.