Its best not to use excessive amounts of wax on leather boots, as it can eventually dry the leather out, resulting in premature wear.
However much wax or waterproofing products you apply to leather, with sufficient amounts of water, the leather will become wet, thats almost inevitable.
Leather is still a product that should be allowed to breathe naturally, and if any wax or similar item is used to repel water, its best to apply it when the boot is throughly clean and dry.
Each to their own, i know, but i just used a high quality boot polish, it was almost as long lasting as wax, and did not effect the leather.
The best all round solution, is to also invest in high quality gaiters, that cover most of the boot, and will keep most of the mud and dirt entering the boot.
Applying a wax product to leather boots, only keeps the weather at bay for a short duration.