We give away tons of stuff from our sites... plasma TV's, holidays etc, current one is 'years free shopping at Tescos' and how difficult is it to get people to leave their details... extremely difficult.
Google 'prize draw' or 'competition' and there are loads of companies trying to entice you to leave your details..
Why aren't people as interested as you'd think they should be? Because they don't want to be spammed, don't believe the competition even exists, can't be bothered etc... age old problem.
I just googled 'sandown park tickets' and your site didn't make the first two pages... if it had done, then I might well have registered, as what you are offering is specifically what I was looking for... and there was only one sponsored link for 'tickets'. I am no expert in SEO or PPC, but maybe targeted activity based on the competition might be a way forward?
HTH
David