Dried out acrylic paint... can it ever be used again?  

Ireally dont think even if you if found some thing that would make soft that it would not work as well and i guess what ever you were going to paint might not look very good,me i would just toss it.

Me, I'd throw it in the bin,

I'm sure that to get some fresh paint would be cheaper, Than the mess and trouble it would take to if its possible back to where you could use it.

But I do that I put the left over paint away for another time, when that comes the paint is useless and dry.

you can try some turpintine or asatone in it to see if it will soften up

I myself came across the same problem with acrylic paint somewhat dried out. I would think that if acrylics are water-based,
then why not add a little water. Makes sense to me. Also for future paints, a piece of glad wrap works wonders in keeping
the moisture in. Screw the lid on over the piece of plastic. Now to try my own advice. Ha Ha. Seashell

This happens to me alot.. and since i HATE throwing my paints out, you can reuse the paint and make it sortof like watercolors [i don't know if that will help you since yours are in tubes} luckily my paints are in small jars...