I didn't know if it should be enabled for text or graphic mode
That depends on which mode you start vl with. If you have lilo as the bootloader, it should give you the options graphic and textmode.
Even if it doesn't, you set the default mode in VasmCC > Service > Bootset.
4 is the one for graphic mode with X.
If you want to start vl on other modes, other thatn the default one, you can pass other options in lilo.conf with the append line, like this, for example:
# Partition 2: Linux TUI mode
image = /boot/vmlinuz
root = /dev/sda2
label = textmode
append = "2 "
2 and 4 are text and graphic modes, 3 and 5 are text/graphic but server modes.
Then you can enable the services for each mode in VasmCC > Service > Services
If your default mode is 4, then enable ifplugd for mode 4 (or for any other modes you might use).
But I guess you've done that already, and still doesn't work, no?