Don't take this the wrong way, but I think your wife has got too much time on her hands,

You can barely see that. I wouldn't bother doing anything. It is what it is. Here's a suggestion: buy a wooden whiskey barrel cut out the bottom, sit it ontop of the cap, and fill the inside of it with natural looking fake flowers. Or buy an old wheel barrel, angle it over it, and fill the wheel barrel with real flowers. If you don't have kids, get one, and that will take up all her time, and she wouldn't then care if that well cap grew.
You could also, sit a birdbath on top of it. My birdbath has a wide opening in its base. Let me know what she thinks of my suggestions.

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