From a Hobbyist's point of view - it is repairable if you have a lot of time, patience and the right tools. Otherwise, buy an Altek and repin at least J# and J4.
Backglass - try with water first. Use a wet rag and keep away from any flaking areas. If the dirt is not coming up, spray windex on the rag. NEVER EVER direct on the backglass. Try a little bit first, and then more.
Playfield - Nifti and rag. Spray on rag. Then use Novus 2.
That MPU is totally repairable.
A bit of patience and some googling will get it done, I am always amazed how repairable these boards are, very simple diagnostics anyone can follow.
It will need the corrosion neutralised with vinegar & water then scrubbed clean and the tracks sanded clean, then maybe another wash and scrub.
Getting all the corroded solder and gunk out of the through holes is the hardest thing.
Playfield may need magic eraser & metho to get the hard ground in dirt out, not too much though as you can lose artwork.
