I guess it really depends on what you think a strength and a weakness are.
Myrtle is rude and a terrible mate because she is a cheater, but Myrtle is very discreet and keeps her secret well:
Mrs. Wilson sat discreetly in another car.
A definite weakness is that when she is with Tom she grows very arrogant:
Mrs. Wilson gathered up her dog and her other purchases, and went haughtily in.
She likes to think she's all that when she's with Tom. I do think it is somewhat respectful not to rub Wilson's nose in the fact that she's having an extramarital affair, but absolutely immoral too.
Wilson's strengths include being hard-working, honest and protective.
A weakness is his stupidity. Tom says of him:
He's so dumb he doesn't know he's alive.
You could argue Wilson's weakness is also a strength. Being unaware is sometimes an advantage in life because you don't have to stress about the problems you just don't know about.