Let's not bring taxes into the discussion. I believe that if a couple have NO children and will NEVER use the school system, then they should not pay school tax. Currently, because I have a house in Pittsburgh, I pay a school tax there (as well as city, county, state, and property) - despite the fact my wife and I live here and we have no kids. But, I bought the house knowing the rules, so I am not complaining.
Sounds like the field trips you mentioned could have been classified as "normal" family activities to me and should have been happening anyway. I mean how many people live this close to the big cities and not take the kids to the monuments, Baltimore Aquarium, etc? Why count them as "school" activities when people do it everyday?