One can make the idea a child of the project. This way, costs/hours of idea will roll-up to project, yet be kept separate.
Would be nice if one had the option of transferring the costs/hours as you suggest. I think the theory behind keeping them separate is that the ideation process is separate cost from the project process – the two processes do different things:
Some would consider the Ideation process the first step of a project – one could would do that within a single project, where the first set of tasks would all be grouped under an “Opportunity Development” phase (summary task). This is still an option for you if you really want all the costs and hours in one bucket. If the resources for each process are the same, might be simpler to just create a project and add “Ideation” stages to your Stage attribute, along with the corresponding items on your WBS.
Just because the Idea object is there, doesn’t mean you have to use it.
Dale