Colorado Blue Spruce Disease Prevention
Is it necessary to spay my Mature Blue Spruce Tree yearly for any potential disease?
Arapahoe County Colorado trees and shrubs
The short answer to your question is no, you don't need to spray your healthy tree as a preventative of any diseases.
Here's the long answer. Blue spruce, Picea pungens, is good landscape tree in our area. They can develop diseases, but generally can fight them off unless they are under stress. Insufficient water, poor soil, and over crowding are some factors that can induce stress.
It sounds like your mature spruce is doing well, and you just want to keep it that way. There are no invasive pests threatening the Blue spruce at this time. (This is not true for ash trees because the Emerald Ash Borer is threatening ash trees along the front range. EAB has not been detected in Arapahoe county yet, so we don't recommend treating them either at this time.)
Here is some information on winter watering your tree. http://extension.colostate.edu/topic-areas/yard-garden/fall-and-winter-watering-7-211/
Basically, your landscape needs about an inch of water every month during the winter months. This last storm provided about an inch of water at my house, so I won't need to water for a while. Just be sure to keep track of our future snowfall this winter because you may need to water.
Finally, here's some information on tree roots and other potential problems that can induce stress upon you tree.