Somehow this always puts me in mind of the famous Mr. Burns line from the episode "A Star is Burns":
MR. BURNS: Get me Steven Spielberg!
SMITHERS: He's unavailable.
MR. BURNS: Then get me his non-union Mexican equivalent!
Based on the Spanish-language tracks on the DVDs, the now-replaced actors do quite a good job -- better than the Spanish dubbers of King of the Hill, who mostly seem to be doing different characterizations than the originals (Hank sounds raspy, Boomhauer talks normal, and Bobby is voiced by a male). Sad to see them replaced.