I don't get it... The elixir only give +1 and each of his stats are in the thousands, what's the point of buying that when he can get helpers, upgrade his dungeons, get items that give much greater stats boost... And gacha, realy?..
Is there a level cap? I can't see how that potion could possibly be worth it if there isn't one. I suppose it would make sense for a game world, though I don't know how they'd justify it "in-universe."