I hear you, lol! I've kind of felt the same way about Drew Barrymore being an off-choice for Brittany, mainly because she's not as young as the other actors supplying the voices; NOT implying that she's too old (because she's only in her 30s I believe), but everyone is like in their late teens to like mid 20s or so.
*Sighs* Again, call me a purist, but I really feel that Ross and Janice should just stick to doing the voices, as do a lot of other people, but then again, according to Twentieth Century Fox, they don't have marketable names (one of the main reasons Ross Sr. created his "David Seville" alias).
Not to mention the fact that, as most people here have already pointed out, Eleanor would then have a southern accent! Reminds me of what MrsPepper once said about how she can still hear my southern accent no matter what kind of silly voice I'm doing.