Agreed, Pearce! I haven’t read the whole conversation, but I do think the best approach is to lay the seeds of Palpatine’s return in 7 and 8, not to make it overtly obvious, but when he is finally revealed in 9, a hypothetical first time viewer would go, “Ahhhh, it makes sense now.” Rather than, “That was not set up at all…”
Don’t make it overt, but don’t make it feel out of left field. Allow room for mystery, like a good crime novel. Mystery surrounds the crime, but when the truth is revealed, you can think back to all the hints that pointed to the truth.