I think the timer wouldn't be so bad if it was just 1-4 hours. A 24 hour span is just horrible, not that I think housing resale is a significant issue in the first place: people were selling at near to placard price before the timer was implemented (with some notable exceptions due to high profile plots such as 11/41 LB, 5/35 Mists etc). In other words, most housing resale was not done for profit but rather to recoup the cost of ones house in the first place without having to wait for the 45day autodemo timer refund.
And in regards to grandfathered houses: I think that the 5-10 designers across all the DCs that own several plots still make up for less of a problem than the sheer volume of people that have houses and leave them empty altogether. I ran around the wards on Mateus recently for shits and the volume of plots that I see where it's just people throwing whatever furniture they have into their house (regardless of size) is huge. I don't mean poorly decorated houses, I mean houses that are deliberately used as storage or not decorated at all. That chaps my cheeks way more than anything else.