I agree just taking a gap year doesn't impress anyone. Nor does doing something "worthwhile" like teaching or building schools or whatever. Gap years are now a business, you pays your money and you take your choice of wonderfully worthwhile, meaningful and important contribution to the Third World. Fron an application point of view, the only reason to do these things is that tutors will not be impressed by someone just taking a year off.
The only time when I think a gap year can really help your application is if it genuinely makes you a better student. And for that, you'd've to do something really relevant. This is, btw, somewhere where I think better off students continue to enjoy a real advantage. I have several friends who arranged themselves long , paid placements in hospitals, with pharamceutical companies of various sorts, even within the offices of a major political party. They achieved this, of course, because they have a parent who's very senior within the organisation. Tutors, I suspect, realise this, but I still think they have to give credit to someone who's worked in a research lab for six months.