The bookable upgrades as I have understood for Gold is limited to ultras-short, short, and medium haul as long as you're a Gold member. However Diamond members receive the exact same "bookable upgrade" but they do not have a limitation due to their tier, not because that their bookable upgrade is any different from the Gold one. So if you're Gold and you don't use the bookable upgrades until you're Diamond, you should theoretically be able to use them on any flight. That's how I have read it. Of course I have no way of backing this up unless someone can speak from experience.

Also I think a lot of people don't realize this, but spending your Asia Miles balance does not affect your qualifications into a new tier. They are separate balances. I get asked this by friends who are new frequent flyers a lot, so I imagine a lot of people wonder about this. Of course the new Club Points and Asia Miles differentiation helps with this.