What's the alternative to buying it? That's an important question. Virtually everyone here will tell you that they think it is, otherwise they wouldn't be on a Civ VI board. Whether it's worth it or not is dependent on what you'll be losing out on, and what you enjoy from Civ 6. Personally I definitely think it's worth the money, but that's me.
You can always disable the XPs, so its no loss beyond money and storage to get them. If you were new to Civ, I'd say okay vanilla first. It's slightly less complicated and less to keep track of, so it's easier. Then when you are confident, move on to the XPs (no need to break them up though, I learned just fine without any issues). Since you already play Civ, I don't think you need to break yourself in.
I don't have NFP so can't speak to that, but the XPs are definitely worth it. I got the DLCs for free, so couldn't say, since they just came part and parcel.