How do people analyze and modify their libraries to make them more useful in production?

Do you compare samples at all velocities within a library to determine problem samples and then replace or change them to better fit the library?

Do you compare samples and programming and modify those samples and settings to make various libraries work together? Do you typically mix and match libraries within an orchestra section (e.g., pizz from one library with arco from another)? Within a given instrument (e.g., use runs or harmonics from a different library for a particular instrument)?

Separately but related, when do you use Mod Wheel crossfades vs. keyswitches? (Mod Wheel crossfades only for swells? Keyswitches only for live play quick articulation changes?)

Also, should you avoid developing/using velocity crossfades in solo instruments, due to the introduction of phase problems...or would the technique work if you kept the crossfade very brief?