notice the 757 has wing fences, does this mean they are buying new(er) aircraft, or is this just to make the 75`s look sexy?
What an uninformed comment. As if they would do something to make the aircraft look 'sexy'. Aircraft aesthetics aren't important beyond the livery as far as management are concerned.
It's to improve fuel efficiency and improve takeoff performance. And as previously mentioned, they are to be retrofitted. Obvious considering the 757s are coming from BA's current 757 fleet, and BA do not have winglets fitted already.