I used he lupo GTI kit for a few years in the mk1. It did the job when i needed it. The only reason i removed the spare in that was to fit a custom sub box and audio install in there so not for a weight reason.
I don't know how far you want to go the weight saving route as theres a thread about it on the other forum.
Back in around 06 when Robin measured the GTI BBS 18s i was suprised they were 12.5Kg and VWs newer versions the Ronals are probably heavier than the previous BBS hollow technology wheels. Thats quite alot compared to something like the 9Kg team dynamics race pro 1.2 8x18 et50 which would equate to a 14Kg reduction.