I was a Silver Hilton member for ages and never noticed any benefit and then somehow I got comped to Gold and it's been brilliant. Since then I've been staying at Hilton religiously and have earned Gold "legitimately" (and I'm quietly hoping that whoever comped me to Gold as a Silver will comp me to Diamond as a Gold!).
But anyway, the upgrades have been great and I've had alot of personal service and individual recognition. I can't imagine how Diamond could be much better than Gold since Gold is so fantastic.