I think if the next movie is going to be successful, it should quickly escape the Batman/James Bond trap. That is, do not make the selling point of the movie it's casting or dinosaurs. It only makes the franchise tired. The only selling points to the Batman sequels were who would be batman, and what (and who would play) the new villians. To it's credit, a handful of the Bond sequels have either provided strong storylines or attempted to expand the persona of the Bond character. Yet the bulk comes down to, who will play Bond, who are the girls, and what new gizmos does he have to play with.
I think JP3 missed a great opportunity to flesh out the role of Dr. Grant. His personal fight with professional extinction and perhaps his reluctance or inability to interact successfully with people (he is basically a loner who embraces his profession with fervor to compensate for his aloofness) could have been explored in his scenes with Ellie and Billy. This personal trait of Grant's may have given Ellie the idea that he had lost interest (when he really hadn't) creating the opportunity for the Ellie character to meet her future husband. Likewise, Grant's enjoyment (though he doesn't show it emotionally) of Billy's company could have really played into the guilt he felt when he thought Billy had died...shortly after Grant had chastised the young man. In such a case, the audience would not just be waiting for the next action sequence. There would some real emotional pull.

One last thought. Many movies had been made where man and dinosaur are thrown into the mix on a deserted island. What made the original book and movie unique was putting this in a theme park setting. I think if JP decends into a cycle of jungle flicks, it will grow real stale/real fast.

And don't ever say that man and dinosaur are thrown 'back in the mix' because they never were in the mix in the first place.

Just a thought...or several of them.