Bit of a necropolis, but I thought I'd share how my own implementation of Spelljammer ship to ship combat went in a playtest I performed yesterday with two players:
I had two players who took the role of elite vampirates leading an advance force as their fleet's home base was approached by hostile Star Moths from the Xaryxian Empire of Astral elves.
Vampirate warriors Dorgio Dali and Vaitalia Daggermore led a group of four fellow vampirates into battle upon giant skeletal bats while the spelljammers Last Breath and Fangtasia followed behind to lend cannon fire. The vampirates and their mounts flew into a necrotic tempest nebula (whose energies they were immune to) to perform hit and run attacks against the enemy advance fighters while the spelljammers awaited the Xaryxian Star Moths.
The vampirate spelljammers and the Xaryxian craft began trading artillery fire as soon as the elves' Star Moths emerged from either end of a necrotic nebula. Eventually, one of the Star Moths closed in enough on the Last Breath for Xaryxian warriors to board and begin attacking the crew members.
However, Dorgio, Vaitalia, and their fellow skeleton bat riders all emerged from the necrotic tempest to themselves attack the crew of the star moth whose warriors had just boarded the Last Breath. They used their bats' paralyzing shrieks and energy drain attacks to wipe out the artillery crew on deck (turning several into shadow allies) while vampirate warriors from the Fangtasia boarded the Last Breath to engage the enemy combatants as the Fangtasia and Last Breath focused fire on the other Xaryxian ship, blowing much of its crew of into space and shattering one of its wings.
In the end, the skeletal bats finished off the pilots of the smaller Xaryxian fighters (which both then crashed into the Star Moth and exploded) while the vampirate warriors scared half of the surviving Xaryxians into teleporting to safety via Word of Recall. The other Astral Elf boarders on the Last Breath all perished as the ship flew into a necrotic tempest nebula, killing the attackers with deadly energies the ship's crew were immune to.
I definitely need to streamline some things and organize better (especially since I'm planning to use this with a regular-sized party and not just two players), but I'm pretty happy with how things went!