IMO, Spelljammer is cool and awesome, but best kept away from established settings. Just like a ship-based campaign works best when there are lots of islands and few major land masses, Spelljammer works best with lots of asteroids and few big planets. Also, while Spelljammer can certainly make use of cool stuff from the Realms, Greyhawk, and Dragonlance, it can be fairly disruptive to the integrity of those settings. If you have flying ships that can encircle the globe in a matter of days or hours, distances are nullified and many exploration aspects of the setting become rather pointless.