Personally, I think earning points through promos should be available to all - and is more in the 'spirit' of the programme. Despite me also thinking the elite perks (aside from ambassador to an extent) suck at present, especially for Spire.
To carry on the the thinking, perhaps an earning bonus for being Plat/Spire. +50%/+100% on top of each reward within the promo for being an elite.
Fictional reward within a promo:
Club/Gold earn 3k for next stay. Plats earn 4.5k, Spire earn 6k.