You're not really getting it though. By putting a topic into a collective thread it is going to be buried, that is entirely unavoidable. This leaves the RITOD thread being only viable for quick Q&A posts or to quickly show off ideas. I understand your reasoning that an ideas section might end up full of n00bs that think it is a good excuse to give someone else the work, or that it will be spammed to hell, but the RITOD thread is not the perfect solution you seem to think it is.
It's not my fault the community acts like that. It's the fault of the community. If you like to share ideas you can post in the thread that is there for ideas.
I believe the Ideas forum shouldn't be about others coming up with ideas for you but about submitting your own basic ideas and allowing others to build upon these ideas.
Just build a set of rules about what belongs in the RITOD thread and what belongs in the Ideas forum and enforce them. At least trial it, because if it turns out to be a failure you can just merge everything back into the RITOD thread and the forums can continue like nothing happened.
Oh and it might be good to move the RITOD thread into the Ideas forum (if you decide to make it of course) as a sticky.