I think Andrew and Sarah, she seems to drop out of sight and he takes the flack, want a 'high-rolling' lifestyle and the younger children of monarchs in this country didn't always have that. Sarah was living the jet-set life at least in part before she dated Andrew and I remember the pictures in the 80's after the wedding of her being seen on shopping sprees in Knightsbridge. Money and the trapping of it are clearly a big thing for her but if she had married Millionaire X it wouldn't have seemed as good as marrying a 'Royal' but she would have had the luxury life she wanted. I think more she wanted the title but she couldn't settle for less than Diana had easily so she over spent. Diana I think wasn't actually that materialistic and was happy with M&S and high street clothes before she married, later the budget was there when she was 'Mrs Wales' to have nice things and it maybe felt like a comfort after a while.
I mention Diana only because the back-story she and Sarah where 4th cousins, with grandparents as 2nd cousins who knew eachother from childhood and they where also friends. I think Sarah wanted what Diana had in terms of the status and financial security but Diana maybe actaully didn't herself. So there was jealousy of Diana from Sarah and then after the Andrew and Sarah wedding Andrew slowly starts to become jealous of Charles and his position but when he was younger he was relaxed and had no issue with it. Somebody has 'green eyes' as the old saying goes.