Are the interviews more for validation or trying to discover what to build or how to build it? Until people are invested in your platform, their motivation to interview is going to be limited. Once you have playing customers actively using it, then interviews are much easier to come by. Alternatively, instead of pitching it as interviews, what if you did "Demos" for people to show them how you could help? You'll still end up hearing feedback and getting ideas, but the focus is more on what your software can do for them than the insights they could give you.
Assuming that your current interviews are more for validation, I'd suggest nothing is more powerful than launching something, no matter how small it seems, that solves the pain well enough to get people to put in credit card information. That's the best validation. If that seems difficult or you don't feel like you're at a point that the product could justify credit card information, then I'd say a good step would be to do what you can to get it to that point.
Looking at your site in the other thread, you're doing a good job focusing on the customer's pain in the copy and the points you have. I'd say I'm pretty well in your target audience, and for me, my instinct for any kinds of promises like this are "there's no way this can possibly work or be accurate." That's not a slight on your software, but rather I know how disjointed all of these tools are.
I'm only one data point of course, but having some information to show how it really works could go a long ways. There's a lot of great promises on there, but it's hard to believe that a lot of them are even possible given the state of the other apps and how they handle things.
The last minor detail is that "Sign Up" might be a little overaggressive in this context. Maybe "Join our Beta List" with an estimated timeframe that you hope to launch could help on that front.