I would consider the web-based gui alternative for OpenVAS to be a lightweight alternative to the GTK-gui-based client. It still runs the same back-end server, but you instead connect via http/s to your server instead of the gtk client, and conduct all activities from that menu interface.
It's called the Greenbone Security Assistant, and is written by the same authors of OpenVAS.
Analyzing cacti graphs of the server show that there is very little CPU usage when managing the system in this manner, and it's stable / usable.