David Hafler 500 power amp..update worth it??

I've had this amp since 1986,with very little use.
It continues to get good reviews despite its age.
There are also several updates available that seem to add life to this old beast.
Is the updates worth it...are they as good as they say?
I'm thinking of selling and putting the cash towards a tube preamp.
Sell or update and use with my second system??
decisions..decisions..decisions..help!!!!!!