Sounds good but my preferred approach for gathering business applications requirements is to start by a high level of documentation of the business processes and their required enhancements followed by collecting requirements for reporting.
We let the vendors use their imagination of how to fit our processes into their applications by working iteratively with the users who will have to rate the vendors based on their ability to meet or improve the business process requirements.
The reports are important because they let every one know what data needs to be captured because it is needed for decision making .. so it often works as an eye opener for all.
Sounds simplistic, yes it is but it works and it is fast.
I have an issue with involving vendors before the requirements are totally collected and documented. Once vendors are in, they want to rush you, they want to influence your requirements, and they find/develop 'friends' on the inside.
This tends to complicate the process from that point onwards.
My preferred approach is not to gather requirements in a vaccuum but to use vendors to present the workings of their solution and jointlyu document the gaps with our team .. saves cost, and eliminates the possibility for users to dream up functionality!