Thrilled to see you having a dip, Rob. Plenty of advise forthcoming!
Removing ball swirl - This is where ME and alcohol is fantastic, as the dirt has gone through the varnish and sometimes the paint. Think of ball swirl as a fine sharp knife cutting through the varnish. Then dirt collects there, the action of the ME removes the dirt and leaves the paint intact - as the varnish is protecting the paint.
Planking - This is where ME and alcohol sometimes does not work as you would expect. Planking is where the wood itself changes slightly. Moisture and heat can affect the playfield creating lines that run with the grain. This problem is not caused by the ball moving around the playfield as with Ball Swirl. I've seen NOS EM playfields with considerable planking, and a ball has never run across the playfield. Planking starts UNDER the primer, paint and varnish. So the paint is easily dislodged from the timber.
When cleaning ball swirl - you move the ME is a circular motion, very lightly and checking constantly.
When cleaning planking - move the ME in straight lines - with the grain. MUCH more lightly than ball swirl.
Addressing planking - you can use the "smear technique" of dabbing paint down to fill the cracks, and wiping with a rag. Good with acrylics. But the theory remains, the playfield will continue to "plank" over the years. You can apply mylar, and this will stop the visible effects of planking. Clearing with a varnish or traditional clear will also hold the playfield together for longer.
As you have already mentioned. You need a lot of patience. Rushing these steps will make the problem worse. My tip is to go a bit lighter with the planking, but be aware that the damage was done by nature, not you. Cleaning the playfield is removing this damage.
