I have $2300 worth of parts on order now for crossover upgrades. Obviously I’m a believer. I also obviously disagree with @czarivey . But it depends on what speakers you have and what their capability is. You don’t want to spend a lot of money on an upgrade to a speaker with poor drivers, for example.
@sns said it well: As long as you're not changing values of components you're not going to change voicing to a huge degree. And the best quality parts are only going to improve timbre, natural sound quality.
--Jerry