I think the main problem here lies with the absence of a more practical substitution policy. At present I think non runners have to declare by end of July - most people who are injured will probably be hoping they will be fit by early Sept and there is still over 5 weeks for other runners to injure themselves.
I understand that the organisers dont really want 500 actually running - this number seems to reduce to around the 350 (which the organisers seem comfortable with) by a combination of the previously mentioned factors.
I do believe that the race is certainly poorer for not having the top runners there - Ian Holmes case is a good case in point and I would certainly prefer to see him in the race. How you legislate however is always going to be difficult. I dont think only allowing people who can beat 2.30 would be fair and that would also change the nature of the event. My solution would be a subsititution system in the same way as 3 Peaks ie within same club up to the day of the race.
Last year Keiron Carr of Clayton (V60 winner) was on reserve list and had at least 7 offers from fellow CLEM runners for their number. Obviously this wouldnt have been allowed and he did get his subsitution via legitimate means eventually.
Guaranteed entry for first 10 and the category first 3 might also help. The debate will continue no doubt