I've payed over $100 many times and would have to say it was worth it almost all the time. I most recently played 7 rounds in SW Ireland last year and all were over $100.
I've done both and picked up information from both. The clinics give your the basics and some tips for practice. 1/1 lessons give you the opportunity to work on a specific issue more in depth.
I have 10 pairs of golf shoes and 6 are spikeless. I tend to use the shoes with spikes if I know the course will be wet. I've found that the spikeless seem to be more comfortable for walking.