Ye they are something like £150 + tyre each maybe your dealership will discount for you! Or wait amd keep a look out on here or ebay and places like that for sets to become available! I want some as well and I have even considered buying a black or white up! Second hand just to swap parts then sell it back on lol but dont have time for that
I don't want to put you off but I would avoid the Classic style wheels. We have currently had two replaced on my wife's car due to corrosion on the diamond cut lip of the rim, I'm also going to be running the car down early next week to get the other two wheels looked at as they are both on their way. The wheels are always protected so you will be hard pressed to keep them looking mint for longer than 16 months.
Let me pop in my two pennyworth, Our Up! Black has now done 19400 miles and 21 months and the Classic alloys are as good as new. Ok, its winter steelies were on for 3 months/2,400 miles, but if the Classics were all suspect, there would be some sign of deterioration by now. As for noise, the difference is negligeable and is probably due to the lower profile tyres - I wouldn't worry about it.
It is not negligible and don't compare noise on summer tyres on larger wheels to winter tyres on smaller wheels. Winter tyres are noisier with a very pronounced whoosh/drone noticable. My winter 15"s are much noisier than my summer 17"s
2dB is a huge amount of extra noise as the dB scale is logarithmic.