Because these are too nice to discard just yet.

I fix all my Beatle boots at TechShop.

Step 1: You Will Need:

Thick leather or hard fiberboard
Contact cement
Rubber sheet
Sandpaper
Hammer or brad nailer
Small nails or tacks
Basic woodworking hand tools (chisel, rasp, knife)
Clamp

Step 2: Prep the Bad Heel

Pull-out the nails holding in the eroded layers. The heels on this first pair are made from several layers of hide glued and nailed. I will be replacing them with more hide. There is also residual glue left behind which has to be sanded off. When doing a pair, sand both heels down to an equal height.

Step 3: Building an All-Leather Heel

If you have a last or a shoe form, then use that. Here I am using a piece of oak to secure the shoe. Use contact cement to glue the hide then the rubber layers and nail them down. It is important to keep the layers tight with no air between so I hit them a few times with a hammer first. The cement should be tacky when the layers are applied, so slipping should not be an issue. Make the bond permanent with tacks or brads. Once completely set, the excess leather and rubber can be trimmed with a knife and finished with sandpaper. If you have an electric belt or disc sander, then use that, being careful not to abraid the rest of the shoe.

Step 4: Alternatively, If Building With MDF

If the heels are made of MDF, then only glue and workholding is involved. Always start with an oversized piece and don't add the rubber sheet yet. Use a clamp that is large enough to reach inside the shoe without crushing the upper (the leather part of the shoe that is not the sole).
Once dry, the block will need to be carved to fit the shape of the heel. Here I am using a chisel to hog most of the excess then a rasp to clean the contours, and finally sandpaper to make it smooth (an electric sander works fine for this as well).
Use the rasp and sandpaper to make the heels level and of equal height. The heel of a shoe is not square like a chimney, it should be taller at the back to tilt the foot forward and distribute weight to the ball of the foot.
Once the heels are right it's time to add the rubber. Start by roughing the contact surface with sandpaper, lay-on the cement, then apply as with the all-leather heel. Here I am holding the rubber on by clamping it with a block of wood until the cement sets. Once dry, trim off the excess and sand.