Spruce Stair Treads
I don't recommend using spruce for stair treads, because it's a softer wood that can be gouged, scratched and damaged with very little effort. I don't even recommend using them for stair risers either.
Spruce is a white lumber with a variety of different
sized knots. Often this lumber is kiln dried and easy to work with. As a
matter of fact, I can't think of one soft wood that isn't easy to work
with. Spruce is an excellent wood to paint and is often used for stair
landing fascia boards and exterior handrails.
Gluing = Excellent, as a matter of fact, every once in a while you will need to glue a knot back into some of your stairway parts, if you use Spruce, for your stairs.
Sanding = Excellent, as a matter of fact, it can be too easy to sand. You better pay attention to what you're sanding, especially if you're using power tools. I've seen sanders dig large holes, in a matter of seconds, into the side of a spruce fascia board.
Staining = Excellent, Spruce is often used for exterior roof overhangs and can be stained with little effort. However, it should be maintained regularly, otherwise it could warp and crack, especially if exposed to high temperatures or direct sunlight.
Nailing = Excellent, it's one of the softest woods I've ever worked with and I can't think of one time, I've ever needed to pre-drill a hole, before using a screw or nail.
Wear And Tear = Fair, like I said earlier, I wouldn't use Spruce for stair treads or risers, because it scratches easily.
Janka Hardness Scale = 480