Rather than tele to base, how bout turn it into a blink? Short distance, random teleport within a limited range seems perfectly fine for the 'Sin.
Tele to base is pretty different from a blink spell. If you just blink a short distance, then you're still in combat, and possibly disoriented, making it useless as an escape spell. Actually, a blink spell would be pretty useless in FreeSpace anyway: There's no way to let people choose where they want to blink to.
However, you just gave me an idea for another spell set.
@Above: The healer idea is win. I was already toying with a summoning spell. I think I'll change Transformer's third spell to summon a "clone" of his current form. I also really like the "Increase skill level of allied AI ships for a time" idea, that's definitely going in.
EDIT: Random idea for Engineer: Maybe I could make everything (except his turrets) work for both sides? That way, if you're not careful, your enemy can "capture" the items you built.
EDIT2: Btw, the first post has been updated.