Just my personal opinion. Ships without Diamond Lounges serve wine and champagne in the evenings. If no club there is a special dining area with specialty coffees brought in and the regular breakfast menu is served Those with dedicated diamond clubs also have wine and champagne, plus mixed drinks and sometimes free beer in the evening hours along with hors dourves. Also complimentary continetal breakfast and specialty coffees.
The Concierge Lounge serves both diamond+ and suite guests with about what they get in the Diamond plus lounge. On Oasis and Allure Ala Carte Menu is served. To me there is a defininte difference in the clientele in the lounges. Check for yourself and see which you like best.