Everyone has that moment when they are graced by the touch of inspirational genius. (Too much?) There have been many an R&D researcher who thought of the greatest ad copy while sitting on the commode, and many a sales rep who came up with the ideal function that would boost sales of their company's product while driving. In fact, there are probably numerous ideas in your company's employees' minds right this moment. Unfortunately, most of these ideas die a lonely death. Let's think of a system that can pick up these ideas.
But wait, it's hardly practical to assume all ideas can be handled by the Planning department. How about if the submitter can specify which department or departments (or ALL departments if that's what's needed) he/she wants the idea to be considered by.
If your company is small or mid-sized (within 100 employees), you can allow all employees to read all replies in case the idea is sent to multiple departments. This should promote cross-divisional discussion. A company that values new ideas is one that can handle changes.