I've also been an avid comper in my time.
I did it for 6 weeks around Christmas 2008 and won quite a few things - a £100 TK Maxx voucher was my first win. Then I won loads of film prizes, with DVDs, soundtracks, hoodies etc. And I won a massive prize worth over £2k - tv, blueray (bare in mind this was 2008, the bluray player alone was worth about £500) and a big pile of boxsets, a cineworld year pass etc.
Then I got bored of entering hundreds of comps a day.
A couple of years later I went back to it.... sure enough, I won a few things but got bored.
I've done this a couple of times and have won some good things, but they are less and less (how can I compete with the £2k prize package?).
I did the advents last year and won loads of alcohol, and nothing else. Not even sweets etc that EVERYONE seemed to have won. I'm not sure I will be bothering this year, but I'll be interested to see how others are doing.
I would say that unless you're exceptionally lucky, you won't win enough to be able to consider it 'earning', or a valuable use of time. But the thrill of a win is amazing.