Both don’t ship with their own Wayland compositor, but there are enough to choose from.
Xfce comes with a wayland session using labwc out of the box, but was also tested with Wayfire. The devs state you shouldn’t hold your breath waiting for the native window manager xfwm to be ported into a Wayland compositor, since they don’t know if/when it will be done. Almost all other Xfce components support Wayland now, while retaining X11 compatibility.
LXQt’s newest stable release has full Wayland support, with 7 different Wayland compositors to choose from within a GUI settings menu: Labwc, KWin, Wayfire, Hyprland, Sway, River and Niri
https://xfce.org/about/news/?post=1734220800
https://lxqt-project.org/release/2024/11/05/release-lxqt-2-1-0/
I don’t think a Wayland compositor needs any more resources than a window manager plus X server.
Why wouldn’t it? Wayland does a lot more. I haven’t done any testing but on vibes x11 feels more responsive on my old system