I sold my Z4 last month without any trouble. Only had it just over 6 months but didn't lose a penny on it. Advertised on a forum and beau and had lots of interest.
I think March is meant to be peak season for selling a convertible as the weather is still bad so people think they are getting a bargain. Personally, I believe that if you make a good job of the advert with good pics (I think this part is hugely important) and pick the right places to advertise it will sell.
If you can't be arsed with the hassle how bad are the prices from the likes of webuyanycar, dealerbid etc?