would make a hell of a lot more capacity, but it wouldn't make much more money, there just isn't the demand for traffic on upgrades of classic lines, unless it's a full major upgrage, WCML for example. Also take into account the length of time you'll be blockading sections of the ECML for upgrades, it is wholy agreed that the lesser total cost solution is a complete paralell route, and this might aswell be a high speed one as most of the associated costs with building a line relate to things that cannot be chaged between a 125mph line and a 400km/h line, mainly land take, perminant way works etc. so the cost to benifit ratio for a brand new 125mph line that will not in it'self generate a signigicant amount more traffic is nothing compared to the amount that will be generated by a 400km/h line.
Especially is HS2 is done properly, and provision is made for 4 track for more of the route into London, the potential for high speed freight could be realised, not nesseserally on HS2 itself, but on the WCML. Also, the idea of motorail services needs to be looked into again, I'd be intrested to know their plans for the Manchester/Liverpool/Preston approach, as a 'Manchester South Parkway' would do well, but as would a 'Manchester North Parkway' and have Manchester served by another branch, also, if international services where to be created, 'airside' platforms aren't too dificult to implement, even if they have the new station in the piccadilly campus, say Mayfeild, or see sense and have it in the Manchester Central or Exchange campus, there is potential for two stations, one international and one domestic as space on the ground in central manchester near other transport links is currently at a premium, there isn't much potential for tunnelling either due to things under manchester that are already undergound, IMO, they'd be best using either a viaduct and/or parallell route to the Styal Branch with Manchester South Parkway in or near the Manchester Airport campus, or, with MSP in the same area, follow the line from Northwitch and Sale into Manchester Central/Exchange with some wider and new viaducts in the city, possibly diverting metrolink to street running in some areas of Chester Road to create the space, or pushing the met onto a new viaduct, but then again, this is the crazy one that would change the majority of met routes back to heavy rail and re-open Central as a commuter station...