The Polipo author's reasoning may apply to your application as well, my memory is essentially the value of HTTP proxies has declined a lot now that so much of the web is behind HTTPS.
Yes. And if it is about HTTP, then the clients' ISPs will proxy the data for them. They may even add some extra friendly stuff in the data, such as ads and announcement banners! The lengths they will go to for their users.
Bottom line: HTTP proxies *are* on the way out, for good reason. -- Laurent