Multiple Residential refers to zoning that allows more than a Single Family Residence to be built and/or improved to accomodate. Generally, such zoning will allow up to 4 residences. For developing 5 residential units (Multifamily Investment/Commercial) and above calls for additional zoning requirements such as parking, setbacks, etc.
Usually the zoning in Mission Beach for example is only going to matter to a developer that believes the real estate economics of the neighborhood justify the time, cost and effort required to either conduct a major physical remodel on the existing structures OR raze existing improvements and build new. This kind of "urban infill development" is often beyond the desires and resources of most interested buyers and therefore not relevant to their buying decision. Unless the development "pencils out" the additional zoning has little or no value to the buyer while the seller would like to assign additional value to such zoning.