1. Upgrading defense buildings has always been a waste of time. You don't get true value on the upgrades, only on the initial purchase, so wasting 1 minute of time to upgrade a building was always a waste.
2. No banking is still a viable strategy and should be your main strategy. If you're a level 73 and somebody 100 levels above you is attacking you, they're idiots. I think you'll find if you're a low level player, depending on how much cash you have on hand, you're not going to lose a ton of it to justify banking it. If I bank 500 mil or so during the war, I'll lose 50 mil. That would take 1,666 losses to justify. Nobody is attacking a low level player that often.