Well with DID/DNIS you can have as many numbers as you want (i.e. Blocks of DID's)
Rotary Groups or Trunk Groups not needed as E&M can come in on any channel. No more busy on main number because other lines in group being used for in/out calls.
Fax hunting. Lot of other options. I am not sure what system you are working with but if you could have DTI card thats the way I would go.