What is the best way to set up specular maps for an iOS game?

We are producing an iPad game - a math game for kids. We have our scene geo set up with diffuse textures and would like advice on the best way to set up specular maps for the level. It is part urban, part countryside environment. Graphics are stylized. The use of specular maps would add a lot to the quality, but we understand that spec maps should be used sparingly and can hinder performance on the iPad.

Do we create them and set them for a lower resolution? Do some iPads and iPhones ignore the specular map if it can’t keep a good frame rate? Is it best to have a separate RGB map, or use the alpha channel of the diffuse?

Thanks for any advice you can lend. This is our first iOS game.