My experience has been that depending on where you work, the certification that you have actually can matter. Now I don’t really know much about NASM, It seems to me that the two most reputable certifications are NSCA, particularly the CSCS (certified strength and conditioning specialist)or ACSM(I have the health fitness instructor certification from ACSM)
Both of these certifications require degrees. The NSCA is more strength and conditioning oriented where you’ll study such things as the olympic lifts and plyometrics. ACSM is more clinically oriented and will serve you particularly well if you want to get into corporate or medical fitness.
Just below those two certifications I would rank ACE which is still highly thought of, less expensive, and you don’t have to have a degree to take the exam. The ACE exam is still quite challenging though and probably is more similar to ACSM as far as the scope of information covered.
That being said, I think you’ll actually learn the most information from practical experience, reading books and of course reading articles from T-Nation.
Quickly Serd I will tell you that you don’t necessarily need a degree to become an effective trainer. However both of the courses of study that you mentioned will allow you to have better credentials and will make you more knowledgeable. Kinesiology is more about musculoskeletal anatomy and will serve you better if you decide you’d like to go into physical therapy, or perhaps even into athletic training. Exercise physiology is more generalized and might be a better path towards academia. Either path would serve you well and give you plenty of options.
I don’t know about average yearly earnings for trainers, but I think even a number woudn’t do you justice. It really depends on the income level in the area where you live, and especially on how aggressively you are willing to market yourself.