"I realize there are other apps out there like this one, but to be totally honest, there aren't many good ones."

Thanks for the honesty. ;)

I'm not sure it's the kind of thing where you can expect a huge number of pre-launch signups. You're providing a tool, but not one that's solving a burning business problem, for example. Big pre-launch signups tend to be for sexy technology platforms, buzz-generating social sites, or useful-looking business apps. Your site may provide value, but I'm not sure it will provide so much value that people really want to be told when it launches. That doesn't mean you shouldn't go ahead with launching it, mind. It could be the kind of thing people only care about once it's there. I mean, if somebody was opening a store near my house would I sign up to get an email when it opened? No. I don't care that much. But would I go in once it opened? Sure, maybe. The two things aren't related.

[edit] Sorry, to be clear: they are related, but not as closely as you might expect. No signups does not mean no business, just like many signups does not mean lots of business.