For those who asked about perks with relatively low flying.

If 25k is bottom tier for One World, maybe you wanna consider Star Alliance, Aegean can get you Gold at 20k per year and it is for 3yrs and I heard if you just keep it active rather than getting 20k every turnaround. Another is Asiana but you do need 40k for the 2yrs every 2yrs. Others are generally 25k for Silver and 50k for Gold. 1 or 2 can be v high ie., 100k for Gold. Gold will get you lounge access if you want that.

If you want lounge access and rewards. Maybe Asiana but you need to keep up with the every 2yr thingy. Because if you do go for the cheap flights, Aegean might only give 0.70 pt per mile, and if you go too cheap some of the flights might give you NIL. This depends on the airline you are flying with as well - as they determine who cannot get points and what can and at what ratio.

Not sure about upgrades. I heard the USA might be easier with that, other part of the world might be harder or near non existent. I heard that AirNZ can be done so .. but tier structure they use for their programme is quite diff to the rest of the world. Put it this way, if you are not a business traveler forget it. You need maybe 3x return USA Asia to just get Silver on economy class.

Also note that BA. I tried to look it up once. I am from NZ and I could not join. Maybe they restrict it only UK or only EU or maybe they not allow some distant areas like NZ.