I also worked in a marketing agency, and we ran the competitions for some pretty well know brands. We had two competitions running simultaneously.
One had a top prize of a fortnights holiday in the Maldives. It was worth over Â£10K, the other had a leather jacket. We got 16,000 entries in the competition for the jacket, and 224 for the holiday.
People get put off entering if the prize seems unattainable.
My sister is the luckiest competition bint ever. She won a holiday to Venice a while ago with Gordon's gin.
I won a holiday for two in the Orient Express hotel in Istanbul a couple of years ago.