My uncle bought a house this summer that had just about everything on the plaster walls you can name, rock, paper, paint x 12, etc. Also the old plaster was cracking and uneven in spots...since it was going to be a rental F it. We 3/8 waterproof sheet rocked over the whole damn thing. Trimmed it out and and used builders beige...looks really good!
Why waterproof you ask? Toughen it up for renters.
If you can I would re rock.