That's the problem, most of the capacity is needed at peak times, and between those times these extra trains will either be running around almost empty or sitting in sidings. These issues don't just effect trains, but all transport, and many other services aswell. Flexable working would really help, by speading the loads over much more of the day. Another problem is the concentration of work in the South East, and particularly London. Surely in a global, digital world, a small office somewhere "up north" could be just as connected as if it were part of a big headquaters in London. I'm sure in most businesses there is little transfer of physical things between departments, most of it will be digital, so there is no need for them to be in the same building, or even the same country.
On another point. I'm sure this investment in extra stock to deal with overcrowding will as usual fail to realise that peak time overcrowding isn't a problem confined to London and the South East, but effects many cities. Also, many lines suffer from seasonal overcrowding, due to additional tourist traffic at holiday times. Travelling on summer saturdays in some areas can make peak time trains around London look quite pleasent, particularly since this can be over considerable distances (i've stood for over an hour before on many none London services). I can't help but feel that this issue is largely down to snobbery, since many of those packed on peak time trains around London are business men and women, wheras those packed onto trains on summer saturdays are more likely working class types, since afterall, the London commuters are going to be on a plane to Barbados, not a train to Skegness.