. My capital ships come out okay, but my fighters always look like they're going twenty miles an hour, even with moving starfields.
Have you considered adding some aberrant motion to the ships? When a fastmoving car swerves a little, there's some back&forth fishtailing, and likewise if you're doing course corrections and such, you'd have the space equivalent.
Having the camera struggle to keep the ship framed (a la THE RIGHT STUFF, which is a good example of selling speed with rubber bands & tape) also might give the speed illusion a bit more oomph.
Yes, I usually have my tiny ships like shuttles and fighters doing some slight side-to-side or up-down rocking motion, and motion blur going on. Where I've not been able to get it right is if they're attacking a capital ship. I never get them moving fast enough to look like high speed craft when the target is in frame. Instead they look like they're out for a leisurely Sunday drive and take a few potshots as they slowly go by. Maybe I'm just staging everything too close together when trying to get the angles I want. I usually render in short 5 or 10 second clips and assemble from there.