I drove the MkVI GTI last week at a GTI Track Day event Volkswagen held at Eastern Creek Raceway. They also had a MkV on hand for comparison. My immediate thoughts are this:

1. If you spend your time belting along at full-pelt around a wet skid pan (or live somewhere where it rains a lot) the XDL feature is worth it. I couldn't say I noticed it on the race track, but certainly on the skid pan it was quite amazing the difference it made (and the MkV is certainly no shabby thing to start with).

2. Aesthetically I prefer the new look in that it has some slight relationship to the Golf styling cues up to the MkIV. I don't think the MkV or MkVI are as good to look at as the MkIV. But as it often said, beauty is in the eye of the beholder.

3. The MkIV interior has the same theme as MkV but feels and looks a lot better quality. It is also less black and gets more chrome work around vents etc. I prefer it.

And that is all that is coming to mind (and I concur with all comments made by others above). Personally if I had a newish MkV I wouldn't be in any hurry to change unless you can't think of anything else to do with your money than to support Volkswagen. I am certain you would get just as much fun and enjoyment from a MkV as you would from a MkIV ... unless you live on a skid pan and are obsessed about interior trim. I hope this helps. Cheers.