The idea behind stainless fasteners is their resistance to oxidation/corrosion. Unless you plan on permanently attaching a hex wrench or other tool to any of your stainless steel fasteners there is no need to worry about the tool causing the onset of corrosion.

With the notion of contamination....this is important when dealing with chemicals. Ferrous material can cause unwanted reactions such as explosions when used in environments where high concentrations of O2 are used.

There is nothing so sensitive about a bicycle that non-stainless tools will cause any issues.

But if you want to empty your wallet for no particular reason then go ahead and buy stainless steel tools.

-j