(setq erc-mode-line-format "%t %a")does the trick and gets most notifications back on the screen.
But then there is still the long-winded away message format. I don't need to have the full timestamp there, so I'm just going to roll with
(setq erc-mode-line-away-status-format "AWAY ").
That makes it easier to quickly check up on activity without having to unset and reset the away message.
Vertical space is also limited, and I don't usually need to see the channel topic. The channel name is already in the mode line.
(setq erc-header-line-format nil)gets rid of it entirely.