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If your scooter has HIC and you want to run standard diameter bars with IHC, you'd need to replace the fork and clamp, in addition to the bars. IHC requires a tapered IHC fork and a standard diameter bars as well as a standard diameter clamp.
I don't have any experience with the Ion deck yet. The Reventon V2 was very strong and they used exceptional computer modeling and testing to design a very strong deck. The manufacturing process has changed since the Reventon V2. I don't know if that means that the strength has changed at all. I'm sure the Ion is a very strong deck as well, but I don't have any hands-on experience with it to verify.
It sounds like you needed those spacers underneath your headset's dustcap to account for an improperly machined bearing cup. This is fairly common. The top of your headtube should go like this, going up: bearing cup (integrated, hopefully), bearing, headset spacers, dustcap, then bars/compression/clamp.
Envy Reaper bars are aluminum, so the only way to run those are with IHC, ICS, or fullsize SCS. I don't recommend ICS as it is a pain. IHC works great, but you'd need to get a new IHC fork. You could probably use your standard oversized diameter clamp from your current setup. Alternately, you could use the fork you have with aluminum bars, but you'd have to run a fullsize SCS clamp (not a baby SCS).