Many people play without the auction rule (hence, they don't even know it exists).

> I seem to remember a similar study from years ago saying the optimal strategy was to always buy if you can.

The optimal rule is a little different: don't sit on cash until a housing crisis.

Just like in a real-life business, sitting on cash that could be working for you is a bad idea.

Another interesting strategy was to not upgrade to hotels in order to create a housing crisis by using up all the houses

Monopoly Junior works like this already - you MUST buy a property you land on, if you can't buy it for any reason the game ends.

It really works when playing with kids, but I noticed that the consequence of it in most games is that the player who goes first usually wins.