mark osterman suggested on his dry plate page
( i have to find it, i can't remember where it is ! )
to use a very active developer and develop the plate for a long time ...

the plates i get the best images from seem like they are over processed
( compared to film or paper ) but they print on a hard paper like azo or lodima &c

hardener is a swell idea (sorry for the bad pun ) ..

have fun!