Part of the value of the kit is its craftsmanship, the limited number of them available, and now that Roberto has passed, its eternal rarity. Value is so subjective, and perhaps to a purist and Spizz aficionado, this kit would be a real treasure.
I've played a Spizz kit, and in all honesty, it didn't sound any better than a well-tuned, nice kit from pretty much any manufacturer. I know that most companies don't offer metal shells in those sizes so there's not an exact comparison, but I didn't find the drums had any special sound. Honestly, I didn't like them.
In terms of it being several times better than a $1500 kit, the answer is no. This is a kit for a collector, not a player. And I know how that works - I have several drums that are more collectable than they are playable, and rarer than the Spizz kit, but I promise I didn't pay $15k for them!
Bermuda