A few years ago, I worked on a HIMSS team to develop a guide for evaluating HIE projects. Now AHRQ has released their Guide to Evaluating HIE Projects to help users assess the impact on healthcare. Evaluating where you invest your resources is important whether you are thinking of joining an HIE or are already a member. 

Also, stay tuned for the March 2015 release of the ONC's interoperability road map. It will also help with your assessment/re-assessment process.