I think you have a great idea! I know exactly what you mean about babysitting your ads on craigslist. I have old bridesmaids dresses (worn once) that I tried to get rid of using craigslist, but it is too much trouble.
Just because it doesn`t exist or you haven`t been able to find a lot of competition doesn`t mean there isn`t a market for it. Who wouldn`t want to save on items like decorations in good condition???
I`m sure a lot of things you could even get for free. Like if you offered to come load the stuff up (clean up), people would be glad to just have it off of their hands and not have to deal with it.
You could network with wedding planners and vendors to offer your services.
Best of luck!