Kopke has historically been among the best at managing price vs sales volume. They have a legendary reputation to protect, and to do so they need to maintain stocks of old wines not just for this generation and the next, but for the ones after that as well. I don't like their pricing because it is very much at the high end of what I can tolerate, but I respect what they're doing because they're doing it well. They ride the high end of the market and have been doing so ever since I've been drinking Port.
Taylor and Graham aren't expanding the market for Tawny Port with their pricing, unless you consider trophy buyers to be an expanded market. And let's be honest about it - £455/$600 for a 75cl bottle of a 50 year old Port is trophy pricing, absent the scarcity of Port from that particular year. And even with the scarcity it is very much out of whack when comparison shopped - I just purchased a 1971 Taylor Single Harvest Tawny, directly from Taylor's wine school at World of Wine (so not in any way discounted), for 255 EUR. That is equally as scarce as a 1972 and felt like a high but reasonable price for what it was. £455/$600 does not feel reasonable in any way, even if they're down to their last barrel. A price like that is for trophy hunters only, not for Port drinkers, and I think that bringing in trophy hunters does not help the market but rather harms it.
That's just it - the only thing "premium" about these is their marketing and packaging. They aren't better Ports. Most of them are, in fact, pretty average for what they are.
Do you really want to be paying that much of a "premium" for marketing and packaging?