Wave 2 has about 200-300 more runners so wave 1 is better. The gate to PP Hwy is new and contains multiple lanes so I would not expect excessive delays that Michelle described. I would plan for them to arrive 1 hour ahead of your best finish time (more if you want to be conservative). They could spend time in the gift shop, have a cup of coffee and a world famous donut. They could also easily spent 30 minutes enjoying the 360 deg views.
Based on your ETA you will spend at least 60 minutes in the final 3 miles above timberline. Last year the race provided near real time updates in the Results section of the website. Your family could get a recent update based on your time at A-Frame. Just being at the finish line in this race is exciting. They have a great announcer that calls out the name of each finisher and often additional personal info like age, hometown, etc. from your registration. I don't think they would be bored if they came extra early.
In response to:
I'm in Wave 1 and am forecasting a 3:45 to 4 hour finish. Would Wave 1 finishers have less traffic and fewer spectators to deal with?