See Sheldon Brown's story on turkey wings (see the entry "Extension Levers"): http://www.sheldonbrown.com/gloss_e-f.html#extension

One of the things many C&Vers do when setting up a "new" old bike for themselves is to rid it of these three offending items (extension levers, spoke protector, stem shifters). The funny part is that, while these are signs of a low-end bike (and thus, an unserious rider--of which I am avowedly one)--changing out these parts does not really do much to make the bike higher end, except perhaps for the cash value of better quality shifters. Though it might make it 1.5 oz lighter, stop better, and easier to shift. OK, maybe that makes it a marginally better bike. OK, the stopping is pretty important. However, as mentioned already, your stopping needs are contextual, and turkey wings don't reduce stopping power in all setups -- just most of them.