Differentiating based on stakes is for people who are too lazy to actually pay attention to their opponents. I've sat at .25-.50 NL tables where open-limping would be bad, and 2-5 NL tables where it's good.

Raising every hand you open is a strategy that works well against people who call too much pre-flop and fold too much to the c-bet. If you're a at a table with horrible players who never raise pre-flop and they stack off with crap in a limped pot, no reason not to limp a lot of hands.