I think by that point it was impossible to break up Mac and Rachel again, and then after Mac died and Rachel went through a period of mourning, Espy was leaving. If he had stayed I wonder if we would have had more with Rachel and Mitch.
I think Felicia and Mitch were fine together, as he was a support for her yet not so heavy that he got in the way of her lighter moments (as Lucas did), but I think Felicia was really too much of a camp construct to ever fully work with a love interest. She was the closest soaps got to the old Crawford/Davis/Stanwyck type dames, who in their 40's tended to feel too rigidly defined to be viable with any love interest.
I never understood Mitch and Felicia. I think he would have been better served in a romance with Rachel. I'm sure the writers did it to stir up conflict between Rachel and Felicia, but it just never worked.
The class conflict could have been done at a couple of different times. With the Loves/McKinnons when they first started taking over the show (especially during Reginald and Mary's returns) and around the time Sharlene and Josie first arrived.
I think they started it with the latter. Josie and Matt on the phone connections line and there was conflict between Sharlene and Rachel. It's too bad that it didn't continue further. Rachel and Sharlene should have been rivals of sorts for years instead of friendly. With Rachel's history against the Frames (Janice's death, destroying Steve and Alice's happiness), Sharlene would have had reason.