So, I decided to revitalize it to bring it back to life.
Step 1: Melt in Hot Water
1. It is flammable
2. Flammable means it will burn
According to wikipedia, it can contain naphtha, lanolin, turpentine, wax and, ethylene glycol. It's not quite TNT, but you don't want to set a flame to it. It'll burn like a spirit burner, but less controlled, and it will ruin your shoe polish, make nasty black marks on your ceiling, and it's not too good to inhale either. So, DO NOT MELT WITH A DIRECT FLAME.
However, we do need to heat it up to get it back in to shape. The best way to do that is to get a baking tray of water, and put it on your stove. Put your tin of shoe polish in the baking tray of water, but don't position it in line above the burner. You want the heat to be indirect. Heat the water up, but not to boiling - about 80C or 175F. You'll know when it is hot enough, because the polish will start to melt.
If you over heat, it can get a bit smelly. That's not a good sign. The idea is to polish your shoes, not your lungs. So just in case, open a window / turn on the extractor fan / do this outside over a camping stove.
If you have more than one tin, you can feed all of the remains in to one batch to make a new whole tin. You can even mix colours if you want to try and produce your own funky shade of brown. I was using natural show polish here though as it shows up better in the photos, and it works well on my grey boots.