It seems that if you jumped earlier on the occasion, maybe the Platinum challenge could've been worth your while. Too late for that though.
In the case that you're not from the US, check promotion central for the Double Elite Night promo, which will fast track your route to Platinum.
And, as Andrew suggested, the Marriott Visa is an interesting option. In your first year the annual fee will be waived any way, but you'll at least get a free night certificate (CAT 1-4) after approval, 15 elite night credits, a big load of bonus points (make sure to follow the elite offer in stead of the standard offer) and you'll be earning an interesting additional 5pts / $ at every time to charge your Marriott-related charges on your card. US card holders even get an elite night at every 3000$ spend, so you don't actually need to go to the hotel to get gain/retain elite levels.
If it's not worth your while, you can cancel just before your first renewal without penalties.