I don't cruise very often, so this might be a different perspective. I ended up getting a last minute super cheap Haven upsell on my 20th anniversary Alaskan cruise ($500pp going from a Balcony to an Owner's suite - I couldn't say no). The experience started from the beginning, which was the separate embarkation plus a lunch at Cagneys - super nice way to start a trip.
The cabin was also super fantastic. King bed, huge bathroom with a tub, two balconies, a sitting room and of course the butler. As someone not used to that level of service, I didn't really utilize the butler very much - but he did do a lot of thoughtful things. He kept bringing us in room snacks and once he realized we liked fruit, he brought us fruit plates every day.
The one downside. The experience feels....isolating. I get that this is the point for many people, but I kind of like being around other people and feeling the hustle and bustle of the ship. I ended up using the Haven pool once, but I was the only one there, and it felt kinda...weird.
But the cabin, if I had paid the rack rate, would have been an extra $4k total on the trip vs the $1k I paid. That would not have been worth it, imo.
I priced the Haven out for the Prima trip to Iceland I am taking next year and it is easily $10K more than a balcony Spa cabin I booked. Not even remotely worth it for me. But if there was another crazy cheap upsell, I would do it, maybe for say, $1-2K more pp. (Won't happen on a new ship, but a girl can dream).