Those accomplishments (or intentions, not clear which) show that you are talented at math, intelligent overall, and have spent a significant amount of your time over the last few years participating in science fairs, with some success. If you achieve semi-finalist in Siemens or Intel, then that will be even greater success.
All that, together with great letters of recommendation, a great high-school transcript, and pretty good essays, will make you a reasonable candidate - in other words, better than average odds. I don't know if you think that makes it a 'hook'. I doubt it makes you a sure thing, but I'm sure it's helpful.