It's useful for demonstrating your problem-solving ability yes. However, it doesn't really seem to reflect your actual aptitude for actual Maths techniques- calculus, trigonometry, algebra etc. For example some of people who got Gold Awards, including the one who got top in the year, struggle with (fairly simple) Advanced Higher (equivalent to A-level) Maths stuff. I mean, the top mark in our year went to someone currently failing Advanced Higher Maths!
So, to conclude, I think it would be useful on an application, but don't expect it to do anything amazing. Being able to solve some fancy numeracy problems won't help you if you can't even manage the basic A-level Maths. Things STEP and BMO on the other hand... now THERE'S some real tests of mathematical ability.