Have all threads come with a poll in which people can decide whether they support the idea by voting 'I support this idea'.

Then, like governments and petitions, if a serious idea gets a certain number of 'I support' votes casted for it, the community manager needs to personally respond to it. If the suggested idea isn't possible, the community manager explains why it isn't and he instead offers some alternatives that could work.

If the manager deems the idea worthy, the idea gets added to the development queue (if it's something quick and easy perhaps it could be done right away).

This idea wouldnt replace the current way suggestions are implemented (the right mod sees the right suggestion at the right time), it would just give ideas another (more systematic) path to implementation.

I think, in addition to this being a good idea, it'd show the community that they're listened to in here.