I'm not a big fan of Aniston either and i know the comparison to Rachel from Friends comes up alot when evaluating her acting chop. Movies like Picture Perfect , The Object of my Affection , She's The One , The Bounty Hunter and The Break-Up do gives that vibe (among others ) .
On the other hand , movies like Horrible Bosses and Derailed are as far from Rachel as can be.
Like Muddy Shores said , she's bankable so far. Hollywood doesn't give big contracts to non-bankable stars. Most of her movies are money-makers.
TBH , i think even Jennifer is aware that her star is fading so she's open to more "riské" role ( hence Horrible Bosses ) ..... she's supposed to show her rack in Wanderlust. ( not accounting for acting capacities , she does look good for a 41yo ).
Personally , i think she's not as stuck-up as it appear .... it's just her agent going for the "if it's not broken , don't fix it" mentality. She did voice a character in South Park after all.