Competitions certainly activate the old grey matter especially where the brief is tight and sometimes restrictive. I well remember being set such a theme. Take a picture that illustrates "Gray's Elegy Written in a Country Churchyard" without the inclusion of a gravestone or a herd of cows!. One thing that it did it made me read it more closely and appreciate it.
I find I haven't got the time or the inclination these days to go out or set up an image between certain dates to find a picture to satisfy the requirements of the competition. I know a lot of people enjoy this and it does impose a certain amount of discipline on your photography. If there is no such restriction I can usually find an image somewhere that will fit the bill. Lazy sod I know.
I've given up those that depend on some kind of prejudging, like DCM POTY, because you bet a pound to a pinch of salt they are sorted by those members of the staff, some of whom haven't got a modicum of photographic nous, and before I'm jumped on from a great height, you only have to see their choices for POTD and the comments they make and the reasons for their choice, and a quick shufty at their galleries. I also have the distinct feeling that there is some 'marketing angle' to their choice.
I go for exhibitions these days, at least they are judged by established judges of merit, but even then they get it wrong, especially in my case!