This is just a personal opinion, but I think displaying level of everyone who is max level is unnecessary, but it's still an option I'd want enabled to see 1. mob levels 2. Someone under max level

This can be achieved easily on line 304 in core.lua:

if ( targetLevel == -1 ) or ( targetLevel == MAX_PLAYER_LEVEL_TABLE[GetAccountExpansionLevel()] and UnitIsPlayer(frame.displayedUnit) ) then

a suboption in the menu might be better: "Hide max-level player levels."

Cheers.