We've done the Illuminations Cruise a couple of times and have definitely tipped well both times ... usually about 40% of the booking cost ... since for both times we've done it we thought the extra services that were done well. When we went Illuminations was before the DS show so they took us back to watch HS fireworks from the boat after watching Illuminations --- while the other boats went back to YC dock immediately after Illuminations. I'm guessing the timing on this will make it one of those YMV based on time of year/availability/ etc...