Depends upon if the options on the "newer" mirror are the same as your original mirrors, and model year of your car. I added auto-dimming, folding LCI mirrors to my non-folding, non-dimming, memory-seating 2008 but didn't have to do any rewiring whatsoever. I had already added an auto-dimming interior rear-view mirror (which required a factory retrofit wiring kit) and did have to code the car accordingly in order to enable auto-dimming of the side mirrors.
If you are adding a folding mirror option, you will need a new window/mirror switch assembly for your door panel (I was lucky in that the seller I bought the mirrors from was also selling a like new switch).
As for aesthetics, I actually prefer the newer larger housing covers over the older smaller housing covers (but yes the pre-LCI's do look sportier)! But since my LCI mirrors were from a factory M-Sport, it did have the lower portion of mirror housing in black "tape" (in addition to having a high gloss versus matte black trim) giving the illusion the housings are smaller and sleeker (I had to have the housings repainted Alpine White since they were Space Gray so I had the shop paint the lower portion black instead of masking or re-applying the factory black taping, so the transition between the two colors is smooth and seamless). As for functionality, the larger LCI mirrors do provide a little more viewing area so theoretically this should offer a little more safety margin.