Adding new planes to an arena full of unperked latewar birds is a waste of time... unless they are more latewar monsters.
Not many of those left to add, but there are a lot of options for mid-war level birds that would be reasonably competitive.
Things that might see some use in the LWMA:
A-26 Invader
B7A2 'Grace'
Do217
G.55
H8K2 'Emily'
He177A-5
J2M3 or J2M5 Raiden 'Jack'
Ju88G (Ju88A-4 needs to be updated anyways)
Ju188A-1
Ki-44-II
Ki-100
Ki-102
Meteor Mk III
P1Y1 Ginga 'Frances'
Re.2005
SBC2-C Helldiver
All of these would be usable in the LWMA and all saw at least some combat.