I have a fondness for stainless steel fasteners on my bikes. I reckon that anyone who has had to wrestle with rusted and rounded-off mild steel fasteners will be familiar with the desire for something better.
Stainless steel offers that option. If, like a few people I know, such fasteners are readily available through their work for nothing, great. For the rest of us, I recommend buying big tubs of nuts and bolts in M6, M8 and M10 as these are the most commonly used fasteners on modern motorcycles. Rather than go mad and spend days replacing the existing ones for stainless, just make sure that when anything gets taken off that it gets put back on using stainless and lots of copper grease. The grease is necessary to stop the stainless steel bolt or screw fusing to the steel housing.