tedhl summarized the tangible benefits.

i am a CX DM member, i do not feel much difference when i mostly fly J class, sometiems F class.

if u always fly F, like GB, there isnt much difference in benefits.

to me, the bests are
1. F lounges in HK, and J lounge when flying into China
2. access AC/FL in NA

now i heard about the gold cart. but they had never offered to me even when my time was quite tight and the gate was near Macau!
(i was only offered golf carts by staff in DFW FL when i flew AA)