So by "affected normally by spells that target permanents" you mean "can be targeted as a permanent", right?
If you turn Rosetta(upped) into a permanent, does its skill change to "Rosetta becomes a creature"? If not, then I think that there isn't really a reason to turn it into a permanent...
Also, I think the unupped version could use the stats of the upped version (5
, 6|4) because as of now, it has the same cost/attack as mummy, but it's much easier to take Rosetta off the field with a 2
Deflagration, a 3
Destroy, a 3
Destroy, or a 4
Steal.