Even if you have students that are already contributing to your project, and just want to allow them to do so full-time during the summer, GSoC is often not worth it.

You need all the mentors available, although they won’t be used, and while the code will be of good quality and kept, the bureaucracy is too much.

One project I (I’m a student with too much free time) am contributing to has discussed entering GSoC before, but we don’t have the manpower to provide the required mentors.