Not sure if I follow Stephen C's logic. A network with city centre stations that runs to OOC which isn't a city centre station. Forgive me but one could argue that what's good for the goose is good for the gander and that terminating at OOC is terminating at London's version of Manc Airport/Meadowhall/Toton which people are sniffy about because they're not central.
I suggested OOC as the terminus to keep costs down, and because with Crossrail its really not that much different in journey times to other London destinations than any of the other termini. Plus theres a fair old chance OOC will be heavily redeveloped to be a new "centre".
In an ideal world, I run those secondary services to Paddington or Waterloo, but extra cost and limited space are major factors. Another option would be Marylebone via the existing line from Aylesbury, (High Wycombe services evicted to Crossrail). But I fear journey times would be extended too far for that to work.
The rest of your comments basically assume people have cars. For many in cities, car ownership isn't necessary. But *all* the existing public transport is radial to the existing city/town centre. Thus, reaching Nottingham station from any part of the city is one bus/tram, whereas reaching Toton will be 2 journeys for most people without a car.