Yep...NO were having weekly sales at one stage. Has been considerably cheaper but waiting for the day when these airlines realise.
Re. Promo. That's the sale fare for 'I' (discount) tickets. They'll invariably be available but the level of discount will depend on the sale event. The last good one (when I booked) was in May/early June. I would expect another one Oct/Nov and then the usual Jan Blue Cross sale and a 2 for 1 (but not really) at some point before the year is out.
As others have stated, the sales are more frequent in other Euro countries. I got a very good price by ex LHR and returning to MUC. The problem with the promo fare is they put you on a ridiculous layover at Doha airport where you're greeted with a pretty uninspiring canteen/lounge. See other posts re. stopover accom but given 6 flights a day to LHR, I fear they'll not be very forgiving.