Thanks again for all the responses! Sorry it's taken me this long to get back about the base plate. The wife has kept me busy with the garage sale preparation.

This is the only significant deformation I could find on either base plate: (B&D)
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And with a pen for an impromptu straight edge:
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After weighing the responses, it seems that the pros and cons of the K-Mart vs. Black and Decker, they come out mostly even. It's power & 2nd handle versus brand & base plate .

Moral of the story: I opted to keep both. They are mostly even. And considering their age, it won't hurt to have a second one around ! Told the wife I was holding back both saws. She blinked at me & said "okay". I already added a couple tools that were either wholly redundant, or not usable for myself (like the Campbell Hausfeld 6" pneumatic orbital sander/polisher, which I have no system to run it on).