It's good that you have an activity like that in your school. I envy you. We also have an activity like that in our school but what I don't like is that the investigatory projects made by our students are copied from textbooks and from the Internet. Maybe you could ask your students to do some investigatory projects which are actually new and never been heard before or I would say new inventions. You can also play some compact discs, Blu-ray discs or DVDs of movies or television or cable shows related to Science and technological inventions and Mathematics. Just my suggestions. Though I am a Social Studies high school teacher.
This year my school participated in the national science fair. We got students to look at the theme and first come up with an original proposal. they looked at time lines, feasiblity of the project and then they presented their proposals at the end of the first semester. the best ones were then choosen to actually carry out the project for the fair. Some needed improvement and rethinking and we gave them that opportunity. In the end we got some really original projects that were relevant to our society. The students also enjoyed the experience.