greater
Yep, that's an option if the situation warrants the expense.
That's a viable qty to amortise the cost I think.
Yeah, it does depend on the requirement I suppose. I did a bit of digging and came up with this piece of current news
I didn't go into the article too deeply but it seems that at least one manufacturer has cracked the problem of plating heavy (up to 6oz) copper for thermal plane application on multi-layer boards.
Yes, quite true. Depending on track density requirements you may have to reduce the track width to a minimum in some areas and in others you might want to keep the tracks widely separated. Thermal planes are a slightly different question but still introduce other problems. There is also the question of emi/rfi susceptibility - too much copper is not always good. I would guess than on many practical boards as much as 40 - 50% of the total copper volume has to be etched away. This would mean as much as 4oz per sqft of pcb using 8oz copper laminate would disappear into the etching bath. That would soon saturate the etchant so you would need a really efficient means of replacing the etchant quickly to do a big run of fairly large boards. Automated pcb manufacturing plants could handle it easily but smaller manufacturers might find it a bit daunting. Increases the costs dramatically.