I'm probably not attending but ..... My sister's husband is from Blackburn and they now live in Chorley. My niece's birthday is January and even last year in the extreme weather we had we were still able to make it across to see her and my sister was able to reciprocate a few weeks later in Feb for my daughter's birthday, though admittedly it was slower moving as the heavens chose to open on her return trip.
Also I agree with Sklark about the clarity of the M62. I too have had one issue with it in nigh on 20 years - trying to get to Liverpool from Sheffield but past Leeds it cleared up a lot and by Manchester was totally clear.
So I don't see a problem for "locals" or relative "locals" I also agree with NotMusimum that the roads would be much worse for congestion etc on a Bank Holiday.
To the potential organisers though you must go with what suits you best and when you can get most attendees from your neck of the woods after all there are many other events available in other areas. To me it would seem silly to choose a date that didn't suit your more local people. If people are willing and able to travel large distances for musical events there are plenty for them to attend and the occasional clash is inevitable
However, for those not willing or able to travel extended distances there's not that much so accommodate your local people first, then throw it open to the rest.
Just my 2p for what it's worth.
And the best of luck with it.