Many thanks for all the comments to my original question.
I read that wheels are one area where manufacturers save money, after all I guess that most people look at chain sets and frames before anything else, so I thought that it would be a worthwhile upgrade. It's interesting that the bulk of the replies suggest this isn't the case, but I still might be tempted, especially by the CERO AR24s which do look very good value. The saving on these from my original Mavic choice would be significant.
I actually think I managed to get a pretty well rounded spec bike for the money (£799) when I bought it, which was far more by good luck than judgement at the time. I'll definitely be better informed when I do come to upgrade or buy new and that's definitely been influenced by this forum. Cheers to you all.