Welcome on the forum.

Why is one image so much darker than the other?

Because the recessed lights are not visible in the second image, probably meaning they don't diffuse any light.

Why are my 'recessed lights' missing in Image 2?

Maybe they are a little too high?

How do I eliminate the 'sparkle' effect on the refrigerator, chairs and oven?

Make them mat.

Is the 'speckling' near the top of the walls a common anomaly?

I think you mean "noise" (yes, like in photography at high ISO). To get less noise, render a larger image then downsize it with any image tool, or use Advanced Settings Photo Rendering plug-in to increase anti aliasing parameters (see also here).

Any tips/suggestions for improving my lighting?

As lights doesn't bounce your ceiling looks too dark, you could add some large lights to fix that as suggested in this tip.