What system(s) did you use to come up with the Khemri buffs and how much of a buff were you shooting for???
From looking at their players I'm a little surprised you didn't adjust some of the costs downards.
For example:
-- The Khemri Thro-Ra is the same price as a Human Thrower with one less AG [huge] and one less AV [big seeing this is a ball carrier]. I'd say Thick Skull and a price of 60K may not be bad at all.
-- The Blitz-Ra is the same price as a Human Blitzer with one fewer MV and one fewer AG. Giving them Thick Skull is great but lowering costs to 80K seems fair to me too.
As far as the Tomb Guardians go I will take you at your word / playtesting that taking off Decay is fine. All that I know is that the Khemri team that I play in "legacy" is fairly tough and would put a hurting on bash-only-teams if the TGs didn't die at regular intervals

To summarize if you raise the costs of TGs [by taking off Decay] then lowering the costs of other positionals might help balance things out .... A lot of it depends on just how much of a buff you're going for though.
EDIT: Lowering the costs of RRs is handy for the team