Actually, IIRC, TheLopez developed an interesting mod involving impacts of resources on tech research rates. It was done for Warlords, but I assume it could be adapted to BtS. It would require tweaking of when some resources appear, of course, but could be interesting. The way it worked was-for example-if you had access to a source of copper, then you'd research bronze working faster than someone who lacked it. Having Cows, sheep and pigs in your cultural borders would reduce the research time of animal husbandry etc etc.
If you're interested, I think I have the files still, and would be happy to send them to you.
Aussie.