^^ Well, for a small, thin crack, it looks like you got a bit carried away with your treatment. Fortunately, silicone is very flexible, but the next time you find a radial crack, just brush the silicon on the crack.
Let it cure for a couple of days and test it out. I don't think you will have a problem, but that was a huge area that you treated. If it has effected the efficiency, then you may require a re-coning from a speaker repair shop. Orange County Speaker Repair is known throughout the U.S (and obviously Australia as well) for the quality of their work and their competitive pricing. Every time I've been there they were very busy.
Your surrounds look fine, but the material on the box itself seems to have degraded in those areas. If those are air suspension or sealed inclosure (not ported), that could indeed affect the sound.
Let us know in a few days how it turned out.