1.Why in the world would someone want to change from a domain that is 2.5 years old to one that is brand new? I would not as you would be basically starting from scratch.
2.Remember not all the pages are driving all your traffic. Have you considered only 301 redirecting the ones that are ranking and getting traffic and forgetting about the rest?
3.Have you considered adding the content slowly? Why do you have to add it over night?
4.Keywords in the domains matter very, very, very little. Changing domains for this reason is a poor choice.
5.How unique are these new pages? Are they just template pages with business addresses on them? If so don’t worry as most of them will probably not rank at all and just be thrown into the SI.
6.Take advice in forums with a grain of salt. As you should not be making this large of business decisions from just reading this thread. You should probably consider hiring someone to help you with this since you are not sure what to exactly do.
7.Here is some 301 redirection help:
Passing Link Juice with 301 Redirects
301 Redirect Resources and Help - Jaan’s Search Marketing and SEO Blog from Cincinnati, Ohio