Not to belabor the point, and not disputing the Lycoming study,
but I think comparing aircraft and auto engines is a bit like comparing
apples and oranges.
The study might be more relevant to heavy trucks, or other engines
that sit idle for long periods and are then run under severe load. In
my case, my cars are usually run twice daily for 30 minutes to an hour
at a time on the highway. (No doubt why I achieve high mileages
without mechanical trouble).
Again, I would never suggest using an engine warming device on a
repeating cycle during a period of non-use.
I don't think ease of winter starting is a reason not to use some sort
of warmer. The old 69 Buick someone gave me sat behind my house
for weeks at a time and always started on the first crank no matter how
cold. It also burned oil at a prodigious rate.
Easy winter starting is a function of compression (so old or worn
engines start more easily), oil viscosity, (could be light, heavy, dino,
synthetic, or nicely diluted with gas) and of course, the condition of the
battery and fuel and ignition systems. Just because it starts easily doesn't
mean it's not harming the engine. And yes, once it's running and the oil
is actually circulating, gentle driving is the best way to warm _everything_ up.
As far as warming the interior for comfort, I haven't seen much in the US,
but Canadian auto stores offer a variety of UL and CSA-approved
permanently-installed interior car heaters, from 500W to 1500W, some
with integral timers.