If there are lots of lights with rather localized effects, deferred shading would be a good way to improve performances:
http://www.ogre3d.org/tikiwiki/Deferred+ShadingIt's used by a lot of games nowadays, notably starcraft II for the very reason that they need to have lots of small light sources everywhere and a lot of models potentially affected by them.
Also, maybe not every light source need to cast a shadow, because that can be very expensive.
Lastly, perhaps evaluate what art really need to use actual light sources rather than just an emissive texture (a texture whose pixels are used as the "emissive" component of the material) or even emissive vertex colors (same thing but with colors painted in vertices, this was a very popular way to fake acceptable lighting on very primitive hardware such as the first playstation).