The linked guide from eh97ac is spot on in regards to tackling corrosion. Get a good size fiberglass burnishing brush/pen and physically remove the corrosion followed by the vinegar treatment. Be careful when burnishing or desoldering corroded areas/components as the corrosion can/does eat away at the metal material which can cause traces to fall off and through holes to fall apart. Such damage may be inevitable but usually can be repaired with a good stitch. I think both boards are viable candidates for rescue but to be honest you should consider the hours and money that will be needed vs. getting a new board(s). It shouldn't take long searching around to find a good system 3-6 MPU and Driver board for a fair price. If you have the tools and can solder well enough this can be a "fun" adventure project.