Do it - you'll save 4k in residuals in the end - compare a 52 plate 25th anniversary mk4 to a "normal" gti !
that's not true. Mk4 gti was seen as an awful gti so residuals were poor because of it. The anniversary was the car the mk4 should have been and was seen as a million times better. The mk5 won every award under the sun and most magazines will suggest the standard gti is the one to go for hence the standard gti having higher % retained value.
If I had the Money spare with no use I would swap. I prefer the ed30
bumpers which really finish the car. Don't expect it to feel very different though. I would not swap mine for any other mk5, the cost just wouldn't justify it.