But there are limits - beyond 457, I'd say most province fights are going to be unwinnable, which means negotiation. Looking at an open 16th-ring province now, it takes approximately 100k each of T1, T2 and T3 goods. Now, I can afford that. I can even afford to do that 10 times, which would be about enough for another expansion. Maybe even two ! But I wouldn't be able to keep doing it quickly, I'd run out of goods pretty soon, and then settle down to a steady rate of maybe one expansion per guest race. And I've been contending for a while now that the one research-expansion we get per guest race isn't enough, Inno are being stingy with them. So this would balance that out.
(and for me, premium expansions are 5400 diamonds. There is literally no way I'm ever going to spend $50+ on that, I spent about that on The Witcher 3, which is a whole 3D AAA CRPG with hundreds of hours of content. A 10% off sale isn't anywhere near tempting me to go premium ever again ... )