I say that because you can buy yourself a mansion for $300,000 with a 3 car garage, a movie theater and a pool.  

Several $2m houses in San Jose is probably safer than a $10m mega-mansion in Atherton (again, just using towns I'm familiar with, I don't know your state).

Also, a sizable number of boomers are selling their McMansions in the suburbs, downsizing to condos, lofts, or renovating the big old mansions. 5 years ago a 6000 sq ft mansion in Indian Village or Boston-Edison was $60-$150K (look at the absurd price now), yes they needed $200-$500K to get it back up to date but people sold their homes to do it with the cash they earned.

They stayed warm due to generating lots of heat internally and only heating the portions of the house being used {i.e. you would not heat the dining room or salon during the night}.With older properties we usually lay-out a plan to improve the building envelope first through air sealing (getting rid of drafts and convection within the wall cavities) and, where possible, insulation {not always straight forward ... many old brick buildings have limited insulation options due to the brick requiring heat transfer from inside to drive moisture from the brick}.Around here it is not uncommon to find an old mansion converted to multiple units - or the occasional purpose-built multi-unit - where the operating costs are 70 - 80% of the revenue and heating comprises 20 - 25% of the operating costs.  

I'm a straight up DIYer so I'd do it myself unless it's a mansion or super nice high end home

Just today I saw a mini-mansion being built next door to a $150K house.

Three are slated for conversion and were exempt from the "Mansion Tax", and the other sold for less than $3 million.

Million Dollar Mansion and this is how I got it

in some markets in the mid west were a 1 mil home is a mansion might get 7k.. but its a white elephant property. 

In the past 2 years, some areas such as West Philly, Brewerytown, Strawberry Mansion, Old Kensington...have appreciated rapidly that they're becoming A neighborhood in a foreseeable future.