On Walmart's store website, it seems like the Pharmacy and Auto Care Center have separate hours and phone numbers from the main store. If services within a store have different hours, phone, and/or website from the main store, I'll generally use separate nodes for each service. By that metric, it looks like the Garden Center node may not need to exist. 
As for the building/node issue, I say we merge the building and node next time the store info needs to be updated. Right now, everything looks correct so no need to change it IMHO.