With SQ, even if you theoretically could upgrade, the fact that Aegean will pretty much never get access to premium award space still renders any attempt to upgrade destined to fail. Which leaves just the intra-Asian routes (and only short distance ones, mainly "intra-far-east"), where booking an award ticket presents way more value than purchasing economy and upgrading (despite the increase in miles that Aegean introduced some 3+ years ago).
I want to say once again, the information about award space (I or O class) being available as a requirement comes from Aegean's phone agents, which could very well be only half true (I was thinking, that perhaps such award requests would clear in a similar way as upgrades with vouchers on Aegean flights do). I don't have any experience with such upgrades myself, but I've learned not to rely on everything I hear on the phone from them. But if wat I was told actually is true, then your *A upgrade options with A3\s M&B are extremely limited as well as over-priced.