Groups (/enable /disable) do not work like that. It's not a form of top-down code execution, but a way to turn on/off groups events like On Text or On Join.

You want to create an alias.

Code:
ALIAS spamchan {
  var %chan = $iif($1,$1,#defaultchan)
  timerSPAMCHAN 0 5 msg %chan $!read(quotes.txt,n)
}

Well. At least I won lunch.
Good philosophy, see good in bad, I like!