In reply to zimpara:
You are asking for short worthwhile routes in modest grades in one of the UK's prime Trad climbing areas that are unfrequented and you are surprised that the well is dry?
Not exactly a secret, but a little less busy than Little Tryfan, Milestone Buttress and Tryfan East Face is
Clogwyn y Tarw (The Gribin Facet) there are some easier slabby pitches there that are worth doing.
If you are not so worried about your "short" criterion you will find some quiet worthwhile things on
Carnedd Y Filiast (Cairn of the Greyhound Bitch) and
Bristly Ridge (East Face).
Glyder Fach (especially the Alphabet Slabs) might also be of interest, but again barely qualifies as off the radar.
There are of course more obscure crags to be found in Snowdonia, but the Ogwen valley is unlikely to be the home to many of them.
Post edited at 10:26