My view from the UK is that you can't
upgrade for minimal (I know it might be different over there, but plenty of UK based readers follow these threads
). Over here I think it would be hard to get more than £3000 for a used X55 (without warranty since it can't be transferred remember), then around £5,000 for another X55 at the current price (making a big assumption that the replacement will be similar price over here to the last one). Remember also that the price difference in the UK between the X35 and X55 is virtually doubling the price for the X55, not the small increase that you can pay in the USA from RS46 to RS56, so our market is a bit different to the USA one.
So for such a small different/improvement that's a major expense IMHO. But if upgrading from an older model or different make perhaps then I can understand people buying one.
Remember it's only IMHO, but sometimes I think the hype that builds up in these threads gets a bit silly, so I think it's important that a realistic opinion is also heard. I got a PM a couple of years ago for posting similar in the RS40 preview thread (IIRC) telling me that I shouldn't post or words to that effect as I'd obviously burst someone's bubble.But we should remember that most updates are very incremental improvements that may not even be obvious in a less than ideal room (ie many of us) unless compared side by side to the old model(s).