In a large city where several of your buildings all require the same resource e.g. Pinewood, it is hard to tell if the current economy you have set up will have a sustained amount of pinewood with all the buildings that require it.
My Suggestion is maybe to have an indicator on all the resources in your storehouse to show if your currently loosing (down arrow) gaining (Up arrow) or keeping a sustained amount (dash) so that you don't have to worry about running out of resources/ running out of storage room for next time you log in.
May be nonviable at higher levels but it would seem to be a nice addition rather than trying to work out the net income of a resource.
Be glad to hear your thoughts on this.