I still have 1 legendary Nightfall and 2 epic Nightfalls left.
So yeah, with 8 Nightfalls and no physical mech using 5 to upgrade my Windforge seems good.
Btw. as my post already stated it is thanks to the gold bonus in campaign.
I only had 3 legendary Nightfalls so far and 5 epic ones.
Thanks to the gold rush I was able to upgrade 3 of the epic ones to legendary and then use them as food.