I guess it depends on whether or not character matters when selecting a candidate. Having close ties to Wall Street calls into question where a candidate’s true loyalties lay. So long as those transcripts are a secret, it’s perfectly valid to question Hillary’s allegiances.
Now, if Hillary ran as a Republican, it wouldn’t be an issue since so many conservatives feel that what is good for Wall Street is good for America. (It would also mean that her party affiliation would match her voting record.) If Hillary wasn’t running for office, it would definitely be nothing worth paying attention to; the fact that she is making money instead of just living off of the pensions she earned as a Senator and a Secretary isn’t the issue here. It’s the fact that she is running for the Democratic nomination for President that makes her paid speeches a big deal.
Oh, there is also the small matter of campaign finance rules. They have some pretty funny restrictions about that, and it’s best to keep things as simple as possible to avoid even the appearance of impropriety, but with those paid speeches, there are ways to do a little creative bookkeeping to evade oversight. It may be nothing nefarious, but it’s definitely something that deserves enough scrutiny to meet some people’s definition of “a big deal”.