Consolidation? Here be Dragons!
I have to question whether the cost of disk storage should be the driving factor here. If the hardware is CAPEX and has already been paid for surely the only opportunity to save money will when it reaches the end of its life, unless a radically cheaper alternative appears? In the cloud this argument makes more sense, as we're talking OPEX and annoying monthly bills for storing stuff...
As for consolidating legacy databases:
Excluding gratuitous clones used for testing and development, IMHO the vast majority of 'overlapping' databases have some pretty good reasons for doing so, usually involving office politics or hard-to-do or obscure functionality that breaks database schemas when you try and merge them. The people who understood the problem in detail will probably have moved on, which means you run the risk of getting involved in a project which delivers no new functionality, might save some money at some point in the future when (and 'if'!) you purchase more enterprise storage, but also has a very high probability of breaking long-stable functionality in exciting ways.
Biting the hand that feeds IT
