For me FP+ was stress free.
Sure you did not always get the exact FPs you want, but with the exception of the first day, I rarely have problems to get FPs for the E-Ticket-rides. Sure it was some kind of stress, but it was 2 months before(!) your vacation and in no way as stressfull as getting concert tickets for some artists.
With some medicrore stress in planning, I could start completely stress-free in my vacation as I knew, I could ride my favourites and could sleep in...
As for additional FPs, the stress level is depending on your choice. I only have a look at the app when I was doing a break, waiting in a line or in the bus when park hopping, but never the whole time and mostly along the way, as I didn't want to stick my head on my phone and wanted a stress free day.