I would certainly agree; doing so (and calling more trains there) would allow the Southern to be removed completely and easier interchange with LO instead.
It is all quite complicated and there are various factors. Back in 1995 , OPRAF demanded the PSR have a 2 trains per hour at the metropolis of Cheddington , which basically set a MK - Euston slow train into the timetable. Fast forward to the same organisation which had let PUG2 with Virgin , suddenly realising that putting all of North London Railways , freight, Connex and "growth" onto the slow lines was a bit challenging. So this gave birth to a massive service recast in 2004 which brought in the present Tring slow terminators. (and a few other things) - poor Cheddington could never muster much more than 1 or 2 passengers a train off peak , and the slow Euston - Milton Keynes was virtually empty north of Hemel in any case. The likes of Leighton Buzzard - would plan their off peak travel around the hourly fast or semi-fast services in any case. Unless they fancied a bit of reading time.
The Connex "Brighton- Rugby - they would have loved to reach New St - minor issues of stock and paths in the Coventry corridor" - settled down to an useful MK - "South Croydon" for which a crossover was installed but really was East Croydon. In passing - the value of this service (in more normal times) for South London to Kensington and beyond and vice versa should not be underestimated. Would be even better used were it able to connect into more WCML services at the Junction.
I would argue very strongly for the retention of a very useful service , as now. If not better.
Watford as a terminating point we have talked about before - you could argue that massive investment is surely needed - apart from missing a North Junction , the terminating moves from the south are awkward and the station is sorely deficient in both ambience , passenger flow capability and the rail / road / taxi interchange is extremely poor. Being very polite here. No one has really run with this one. What do you expect though for a town that sold its soul to the motor car in the 1980's and all sorts of other "recent" pressures on retail etc make it a case for some serious TLC and investment. (subject to funding "cough")
Willesden Low Level main line platforms were looked at quite hard in the mid 1990's - it could never have happened then - especially with the late decade capacity questions , - and even post HS2 I would challenge it's worth. A change of a very frequent service at Harrow and Wealdstone changing to a much better DC / Bakerloo line - the latter will have new trains hopefully , and the former has , is no great hardship. IMHO. Some money could be usefully spent on H&W station.
Issues of pathing Bletchley - MK seem to drive a lot of debate , which is a good thing. I have my own views - but let us see what comes back.