With <25k per year, it is not obvious to me that trying to stick to one airline is your best bet. At least, I wouldn't pay a big premium (no more than 10-15%) for flying with "your" airline. You can also look at who has the best promotions going on.

I had your travel pattern for years. After a while you start getting that free trip every now and then even without being loyal. After all you accumulate miles at the same rate.

If you think you may be able to reach a status level then it makes sense to be a bit "more loyal".