I think Rafe being madly in love with Carrie and the quick change to Sami is just due to the writing staff changes – and I welcome them!
I think Lucas coming back made sense – for the Will is gay storyline. I think the brief Lumi do-over again was due to the writing change. Perhaps having Lucas back now, he can be developed as a character – his relationship with his mother, maybe help his half-sister Jennifer thru her loss, as a parent to both Ally and Will (two "children" whose needs are very different), and maybe even in a career wherever he is now working. I think it would even be better if he stayed on at Countess W with Sami and they were friends (without the benefits) and business colleagues, and coparents.