Before we write off traffic from Plymouth to the north of England as a niche market, may I add that those trains have significant value in the other direction: Devon and the so-far-not-mentioned Cornwall are major holiday destinations who receive a lot of visitors from the north, and having direct services from Scotland, the north of England and the midlands is still valued accordingly, particularly as we would like fewer visitors to come by car.
Changing at Birmingham or crossing London are fine for the train-savvy, nimble and time-sensitive, but less attractive options to anyone juggling kiddies and holiday luggage, even if the direct journey is slower. It's not just the inconvenience of switching trains: it's the uncertainty of making the connection and losing booked seats together.
It's clearly true that travelling north from Birmingham itself will be quicker by HS2. But on journeys between the south coast/south-west and north/Scotland you need to factor in the inter-station transfer and suitable connection allowances, so changing at Birmingham to HS2 for services north won't reduce journey times by much in comparison to the overall journey time, and through trains to the north will remain an attractive option.
And given that CrossCountry certainly used to encourage people to change at quieter stations outside Birmingham to reduce crowding and inter-platform transfers at New Street, I wonder how sensible it would be to force everyone off every XC train at that station, particularly if more people are alighting there from the central core to switch to transfer to HS2 for London, rather than continuing to allow many to travel through.
So to answer the original question: yes, long-distance direct still does have value for those of us at or near the extremities. And yes, it would be nice to have a wider range of links to and from both sides of the north. Like we used to.