If you are in such a situation where you now have to maneuver around the cheapest fare with your choices and stay within a 15% "orbit" then I would look at only two things:

- flight times/schedules
- reaching/renewing status and making use of FFP benefits

If you don't care for IFE or food (I put some emphasis on the former, though I'm with you on the latter and prefer to eat pre/post flight), then I would certainly look at flight connection times, choice of transfer airports, departure hours, etc. to make sure your trips are as hassle-free as possible. I think this will help out more than the difference between a BA or LH econ seat for example.

Apart from that I would concentrate on status and all the benefits that come along with it. Look at how many miles you will be clocking up each year and go with an airline+FFP that will reward you with status. This can make a HUGE difference, especially when flying in Y. You would potentially be looking at business class check-in, extra luggage allowance (useful if you can get a bit of shopping done on some of those trips), lounge access.

One more thing I forgot about which is quite important is seat selection, especially in Y. Some airlines will let you choose your seats without any hitches, others will charge you for it unless it's OLCI time. Status could also play a key role here, which is one more reason to concentrate on that.