It can be fairly frequent a this time of the year but probably not enough to justify significant investment. I believe they installed some equipment a year or so ago that checks the visibility (previously done by a man on a ladder) which seems to have resulted in less diversions. The runway lighting system must be due an upgrade though. I wouldn't be surprised if it is the same one from when the airport opened. A grooved runway like SEN would also help and the runway must be due a resurface. Small things can be done to improve things. The armchair experts on here thought Embraer's larger jets could not use the stands parallel to the runway but we have now seen a number of BA ones use them. Clearly they made changes to improve the operating environment.
On a side note, I see the demolition of South Stoneham House is about to happen. Its a 17 story tower block which 20 departures to the north fly over. I wonder if this will help runway performance a little bit.