Trust me people it'd take more than 3000 signatures to convince Disney or any movie producing company for that matter. Most movies take AT LEAST a couple million to make and sorry to say that 3000 people who guarantee to come won't make up for it.
It is true that more than that would show up regardless (I mean most people who want another might not know about the petition) but they'd still need enough support and facts that show that a majority of people are going to show.
Besides one question we all should ask ourselves is 'do we want another Land Before Time mess to start again?' because odds are we wouldn't, no one would, I mean what number are they on now? 19 or something?