When I first started out, back in the mists of time, rehearsals were also/mainly about learning your craft, with not a lot done as homework, by anyone (we were kids after all). Once I was older, at a good standard and playing with good bands, rehearsals were mainly there to try new songs that we would have learnt at home to a certain arrangement and seeing how that proposed arrangement worked in the flesh (obviously for any new band members, this would mean a complete run through of the set). They were also used to sharpen vocal arrangements. However, we would also revisit older tunes as a warm up or if someone wanted to try something different in a particular tune or, as you say, iron out an error that may have shown up previously.
"It's just the very late gigs and packing away are the downside (but nescessary evil)." Yeah, that very much for me too. Plus the waiting around beforehand, even at home used to get to me, it seemed like dead time. I'd rather an afternoon gig, where you could get up, get ready, get out, gig, maybe socialise a bit after (rather than in a dark car park after a normal gig), come home and relax at a respectable time. For this reason, I always liked rehearsing (we tended to do Sunday afternoons), it was relaxed, easy going and also a great catch up with folk I liked. I miss those days as I'm currently bandless.