Action-is it too high?

Hello Dulcifolks!  

How does one know when the action of a dulcimer is too high?  I own two dulcimers.  One of them is much easier to play than the other.  I feel with the other that the bass string often gets muted or sounds unclear, and in general I have to exert a lot of effort to press down the strings.  

Not sure what I'll do if it's the action, as the nut is super-glued down!

Would appreciate any insight from those more experienced than myself.