There is a major chicken and egg problem here.

As a post-YC company, I know a lot of investors. That means my gmail is valuable to you (since you can pull a bunch of info) but that your service is not valuable to me.

You need to better incentivize users that have the information that makes your service more valuable. Something like AngelList's ability to verify that an investor invested in a company, plus the ability for founders to anonymously leave reviews of investors that you confirm they've spoken with.

If, going into our next round, I could only access those reviews by connecting my work GMail, then I can see why it may make sense.

Right now, I don't know why I would use this and I think I'm your target market.