We are required to do 120 here, though there is no limit on how much we actually can do. If I wanted to I could have studied two degrees at once - was what I tried when I took on board the extra subject, but it was a bit too much for me.
One entire semester just to gain an extra 3 credits does indeed sound like it is quite worth it to rather take on an extra course. However, I have a feeling that if the others were reading this forum, we would have several objections regarding you "going mad", with most of the objections centred on the word "going". But I am nice and shall not comment on it :-)
Ran into an old professor of mine who has retired by now when I was in church last Sunday (got this brilliant priest at a church here, very much of a leftist political activist, gay and prays for Palestine rather than Israel). Mentioned to the professor which subject I'm hoping to write my dissertation next year on, and his first question was whether I was "driven" to research it, being as that was the only thing which matters. In his case when he did his PhD, his wife was convinced he was mad being as he talked so much about it. So yeah, best find something you are interested in rather than just do it to continue sutdying. No point in spending 4 years on something you don't like. As for getting accepted, don't know how you are doing academically but from what I've seen on the forums my guess is that you stand quite a good chance there if you do find something you are interested in.