If you have the ability to fund substantially, and the experience to build $9,000,000 in revenues, why would you sell ~5% of your company for $15,000?
Paul Graham(ish) tech. wisdom, networking opportunities, mind-sharing with past YC founders and VC connections if/when time arises are all huge.
And for me personally all of the above are important X 10 because I'm a tech & SV outsider just beginning to build my shere of influence in the sector.