Going from plain to Gold to Platinum rarely brings any extra benefits,
other than it being loosely linked to the credit limit, but even that's
not guaranteed.

Depends on the card. I have a green UK Amex card, and there are certainly
benefits I'd get if I paid for a fancier card, although I don't think any of
them are worth what they'd cost:

http://www.americanexpress.com/lacid...ss_cards.shtml

I have a mastercard from HSBC UK, which also provides travel cover. I agree that the
differences among their cards are much less interesting.

R's,
John