Your willingness to share your efforts with others is a generous gesture; which makes it even more unpleasant for me to be the one to pee on the picnic. :(
Vangaurd's condition of use here:
{Link removed, see update below}
"Except as otherwise stated in these Terms of Use or as expressly authorized by Vanguard in writing, you may not (or enable others to):
Modify, copy, screen capture, distribute, forward, transmit, post, display, perform, reproduce, publish, broadcast, license, create derivative works from, transfer, sell, or exploit any reports, data, information, content, software, RSS and podcast feeds, products, services, or other materials on, generated by or obtained from this Site, whether through links or otherwise (collectively, "Materials");"
They also have very specific conditions governing how you can link to their site (at the same TOS URL).
I don't think anyone who is using your website is in violation of these terms; however, I find it hard to imagine how your website is sourcing its data while remaining TOS-compliant, assuming you don't have a written agreement with Vanguard.
Certainly not a condemnation on my part. Just an FYI.
I plead protection under the bearer of bad news articles of sanctuary.
Update to add: It turns out that even linking to their TOS page here is a violation, so I removed the link. You can find the link I removed by searching Google: Vanguard Terms and Conditions of Use.