Does the bonus from a shield have any affect in lockdown

They are from people crafting them for the sole purpose of selling them. One of the good things about buying a recipe is that it is not only cheaper than buying the item itself, but you can then use the recipe to put together those raw materials again to make an item to sell, hopefully for more than you would've gotten for just the raw materials. Note that crafted items will sometimes get special attributes that you can't get on dropped/store-bought items, making them even more valuable.

There are two sides to this, depending on whether you plan your path or not:

Because the Clockworks is constantly moving, even when you're progressing through a level, you have the option of deliberately waiting to step onto the elevator in order to reach desired levels. Each of the levels has a (usually) pretty obviously descriptive name reflecting the types of monsters you will encounter, and since gear with fewer resistances is stronger against each source, you can "stack" your resistance to a select few and plan out your path for maximum resistance. They hide the option to show the gate map under the upper-left menu with no way to hotkey it, but it will show you where the elevator is currently pointing.

For the more casual player who expects to face damage from a variety of sources, pieces with multiple resistances will help negate more damage on average than a specific piece. Because they have more individual resistances, there is a greater probability of entering a level they can resist some of the damage from, rather than limiting all of your potential resistance to a single source and missing it.

The bottom line is that very few sections of the game actually depend on your gear's type enough that it makes a significant difference. As long as you have enough stars on your gear and a fair amount of experience with the enemies' tactics, you can just pay attention to your "threat meter" to the lower-right of the minimap.