Dinan Stage 1 here. My car was an early build '07 and didn't come with the factory oil cooler, so no Stage 2 for me. I got mine flashed at the 20% off rate at the same dealership I bought the car. It was about $1600 out the door including 1 hour of BMW's high labor rates.
I did read that if I were to eventually install the oil cooler, I would be credited the full price of the Stage 1 towards the Stage 2. I'm not really sure that's necessary, as I've been very pleased with the performance increase and it more than suits my daily driving needs. But is it really ever about need?