Yes, when I was a Nicholl's fellowship quarterfinalist a few years back I sent out hundreds upon hundreds. I got a bunch of responses which was honestly based on the Nicholls placing and not some great query I wrote. Honestly, you need to get that out of your head regarding "Who will respond How long will it take for them to get back to me, etc." It can range from a few weeks to never, even after sending the ma follow-up email a month or two later. I've made a few contacts but people don't really get back to you much.
I don't trust any of these mailer or pitch sites. Although I tried VPF for a TV pilot. I got a bunch of requests from producers, agents, etc. Whether it's a mailer or pitch site it's low-level assistants representing the agents/companies & are the ones that are gonna read your script or just the first few pages and toss it out. All these agents, prodcos, managers, etc are mainly on these pay to sites to just be visible and to say they are n the and because they get some money out of it.