Often the purchase of electronic materials is justified first by weeding out library expenditure that you just don't need. Examples are areas of law you no longer practice, or want to practice in, and reducing purchases of parts editions of some subscriptions. Duplicate sets of materials that are replicated in databases can next be removed. The final decision, once the electronic materials are firmly entrenched, is to cease equivalent hardcopy subscriptions. When considering any information project there seem to me there are 3 basic smell tests over and above making it fit the general business direction.
Finances Making the numbers is the first hurdle.
One important shift is away from defining value from having to using. When purchasing electronic information, the value of having seems to diminish. The real value you get is when you use it. I don't think the value formula is all that clear at the moment. However, buying electronically does help focus this issue.