It might be that someone has already done this, but I couldn't find the file so I made my own C3C resources.pcx file that shows resource icons and happy faces for luxuries without changing the graphics of the resources themselves.
And here is the file: http://www.civfanatics.net/uploads7/ImprovedResourcesC3C.zip

And here is the file: http://www.civfanatics.net/uploads7/ImprovedResourcesC3C.zip