I completely agree - it's like retroactively applying highly restrictive zoning laws after someone's bought a home - likely reducing the value of the property.  

A fairer approach would be to apply the same zoning laws, regulations, designations, etc. across the whole city.  Then, an existing owner or a new buyer can decide to designate his/her home as historic.  Subsequent buyers would also be subject to that designation, and know what they're getting into.

However, this will probably never happen, since urban Leftists don't really believe in private property rights - they would rather just pass laws that tell other people how what they can and cannot do on 'their' property.