Welcome to FT, rosierd!

So you ideally want to redeem miles for a first class ticket and fly mainly economy, right? In addition to the advice Mwenenzi has given you, which I agree with, I think you need to focus on US-programmes rather than European ones. As you note, BAEC is not really designed for infrequent economy fliers. You won't earn a great deal of Avios, and redemptions are difficult due to limited availability and very high YQ surcharges. Lufthansa is really not much different. They are increasingly designed to target high- and frequent-spending business travellers.

Have you thought about UA? The airline is never going to win any awards, but as a Star Alliance member you have fantastic European earning potential and pretty good availability to the US and beyond in the business and first cabins for redemptions. They are also usually cheaper on flights to the US.