I'm a great believer that garden tools should be stored clean, dry and warm. Garden tools live a precarious life close to soil which can be cold, damp and dirty. Prolonged contact with this stuff can lead to corrosion. The rust is bad since it leads to irregular pitting of the surface of the tool. And the more the surface is irregularly pitted, the more resistance as the tool travels through the soil. Since digging is done with human power, more power is needed to push the spade into the soil, meaning that a gardener can be more tired at the end of the day than is necessary.
The other thing about a tool which has a rough surface due to pitting is that soil sticks to it more readily than if it is shiny. So in any operation where you want a tool to travel into the soil and come out clean, a rusty tool will work against you. Take ordinary digging. You push the spade into the soil, lever back and turn the spade so that the spadeful of soil is returned upside down. It should fall off clean with each dig and turn, but the soil will not fall off completely if the surface is rough so that the soil can stick to it. At each dig you have to stop and use a heel or trowel to clean off the spade before you can use it again. Instead of digging an acre a day you will only dig a tenth of an acre, be ten times as tired and receive only a tenth of your pay.
The design of a spade can affect how easy it is to clean. The goal is to minimize the places that soil can stick and accumulate. A welded-on foot plate in this sense is better than a blade which has been simply "rolled over"; the rolling over creates a ideal place for soil to accumulate which can only be cleaned out with a stick or a nail.
Over time, wear on a spade will thin the blade due to abrasion by soil particles; the thinning will be good from a point of view of penetrating the ground but clearly weakens it in a prying situation. In addition a point will become less pointed as the point is worn down.
You can consider stainless steel which resists corrosion, but consider its hardness qualities too when the spade or fork is used in a prying context. Ted Irving has some thoughts on stainless(1). I have no experience with that material so will refrain from commenting on relative merits.
(1) http://www.victoriarhodo.ca/Archives/Irvng304.htmCopyright © 2016