More does need to be done with the MML. As with the ECML, it needs to be quadrupled along as much of its length as possible, and electrified from Bedford to Wakefield, including the Derby loop & Nottingham, possibly all the way to Grantham.
It also needs a full 'WCML upgrade' esque treatment to ensure 125mph along the whole line, preferably before the arrival of the IEP, after which it can be used by the then-redundant 91s & Mk4s.
However, what wil count against this is that (in my opinion) the sensible route for HS2, following the old GCML will serve all of the places the MML does, with Sheffield being the first major stop, and one of the bigest junctions, being where trains for Manchester & Liverpool diverge from trains for Leeds, Newcastle & Scotland.
What it does make abundantly clear is that we need a long-term plan for investment in Britain's main lines. The MML & EoEML both need upgrades to increase speeds between centres & provide shorter journey times. The ECML needs rewiring as the present OHLE is, as is often said by NR staff, unfit for purpose.
Finally, the GWML needs electrifying through to Swansea & Exeter, with the old LSWR mainline reopening to serve Plymouth & Cornwall under wires; the West of England Main line could also do with being upgraded & electrified from Basingstoke to Exeter St Davids to provide an alternative route to Exeter, as well as better links from the south west to the south east.
This is all going to cost a hell of a lot, plus the HS budget. But what needs to be realised is that, while HSR will boost local & national economies, it will almost certainly remain expensive. Therefore, improving conventional rail services, and ensuring that their prices are competitive for the leisure market, is key. If someone can get from Sheffield to london in 90 mins using a high speed service costing £70, all well and good for business & well off travellers. But if the opportunity of a 2hr service costing £20 exists, it will open up long distance rail travel to a far wider range of people, which is vital if rail is to increase its modal share.