Most real disasters are much less well-structured than a test - so if you can't make the test work when you can plan for it in advance and stage everything just right, what chance will you have if the big one hits?
One way to get a workable DR plan is to do some up-front scenario analysis after the BIA is done and build up a set of layered responses to incidents of increasing severity. For the least serious impacts you can engineer high availability solutions - essentially disaster avoidance strategies. For disasters you can't avoid, you can build routine operational processes (things like rolling cluster upgrades, managed application failover, deliberate load shifting) that let you practice for a real problem, so your people are familiar with most of the work they'll need to do in a disaster. That will also exercise most of the technologies you'll need and ensure they're working reliably - and that the disaster won't be their first use.