Actually you should really regularly update your firmware (or keep it up to date along a baseline), particularly for things like c-class blades and the network interconnects and particularly if you're environment is quite dynamic (e.g. OS updates often, e.g. Linux point releases) and hardware gets upgraded, moved etc. However, you should make sure you talk to HP to work on a method here, since there is a "compatibility matrix" of sorts for these things.
Ensure you're on the advisories for your products, this will also determine what you do.
Same applies for firmware as it does for PSP.
Note - HP also looks to release a quarterly firmware and PSP bundle which they recommend is tracked.