In my opinion it's not smart or worth replacing everything with stainless steel.
There are numerous grades of stainless hardware, the cheaper stuff is weak. The good stuff is quite expensive, it's not always easy to know what you're getting.
Stainless is prone to galling, especially when used with stainless nuts, so anti-seize is very important.
I do like to use stainless for little details, trim screws, non critical stuff that is hard to keep painted or not painted at all. I wouldn't use stainless fasteners for critical engine, suspension, brake, or frame hardware.
Grigg
