I've used a simple grid to prioritize e.g. risks, brainstorming ideas, etc. For detail prioritization you could use a 3 x 3 grid, one axis being cost/effort (rate as low/moderate/high) and the other being need ("Nice to have"/"Need to have"/"Critical to have"). Ask the sources to independently rate the items they gave you using these criteria, collate the results and put them up on the grid. An example from a risk management exercise is:
You should get a good idea of what you should prioritize at a macro level doing this, and you can modify the results a bit based on your business rules (e.g. customer's criticals come first) to make a sensible final list.
You can also develop rules for which details will be addressed and to what degree. In the risk example a business rule might be to accept risks in green boxes, mitigate those in yellow and actively avoid those in red. In your case, a low utility/high cost item would be scoped out, high utility/high cost items would be assigned your top tier developers, etc..