I'm not sure it needs to be a well known act, but the UK would do a lot better if it put forward songs of any substance. I feel as though the problem in most recent years is that the UK songs have been plodding numbers that go nowhere and have nothing memorable about them. This year's German song was bad, but it was gimmicky enough to earn a handful of points, whereas the UK entry was the sort you'd forget about immediately after hearing it.
Name value probably helps a bit, though. The UK finished 19th in 2013 with a characteristically dull song, and I'm sure it would have come last or thereabouts if it hadn't been sung by Bonnie Tyler. Similarly, Blue finished 11th in 2011 (and 5th in the televote) with a pedestrian entry.