I'd like to present my little idea for what you can do with icons. Instead of just one type of thing, you can do two things with icons. It goes like this:
Collect 11 Icons of one Giant and combine - Create a small 'Temple' for that Giant on your home street which you can go to and pray at or something. Depending on the giant, you'd start getting more iMG bonuses for associated skills.
Collect all 11 Giant Icons and combine - Create the 'Mind Talisman', a sacred object which... I dunno what.