I have only been a crew member on a single ship voyage as there are only a few ships constructed with many currently under construction including TOGs first ship due in about 30 days. Ships can be outfitted with enhancements found in the astral, including weapons, engines and shield/armor.
Ships are the only way to travel to most of the astral which is a hge portion of the endgame in Allods Online. They encompass not only a means of travel but allow for combat in the astral against group and raid bosses as well as other ships. With time this will be the focus of player vs. player combat in the game and it is my understanding guild ships or raid ships with larger crews will be able to be constructed.
The ship component of Allods is definitely not fluff or filler content. The astral has over 30 zones with mutiple objectives in each area. These objectives provide legendary gear and large amounts of gold. Playing the endgame of Allods without access to a competitive ship is missing a large part of the game.
At this time navigation and combat can be a little spotty, but hopefully this will improve with upcoming patches. Right now there are three astral demons that have been encountered... one is too easy, another far too dificult for any constructed ships. And, the astral raid bosses are reported to be very difficult for currently outfitted parties. With guilds progressing through heroic dungeons, endgame raids and astral encounters the content should be more manageable.
I hope this answers your question and hope to see you in game.
"It is pitch black. You are likely to be eaten by a grue."