The Grand Central proposal would also have been sited where the existing lines are. And have the benefit of being able to accomodate more and longer platforms than New Street as well as approach tracks from one side at least. Terminal designs are unnecessarily limited when all you need to do is build a station with the means for the tracks to be extended at a later date. HS2 seems to deliberately prevent this possibility.
What seems to be overlooked with our existing inter-city services is all of the smaller journeys between regional cities they allow that on their own wouldn't be much of a business but together work well. Getting from Newcastle to London for example currently is fine. But being able to get from Newcastle to Edinburgh, Glasgow, York, Leeds, Sheffield, Birmingham, Manchester, Liverpool, etc is also very important and it's the same for other cities. I'd rather we had some grand plan for these connections before anything else.