[ALittleLight]

A good change in rules is prohibiting people from buying with the purchasing price - i.e. every property is sold at auction. Best to also do a single round silent auction where the winner pays second place's bid (e.g. I bid 200, you bid 100, so I get it for 100).

With these rules you will quickly establish that some properties are not worth buying. These rules also have the benefit of making games ~30 minutes long because people run out of money extremely fast.