No doubt that deferring maintenance is a recipe for insanity and I believe it was one of the major reasons for the company going belly up.
Crew size, on the other hand, did not lead to this problem. First, unlike Agressor (which you mention), the Nekton Boats were US flagged vessels. Having a US flag requires a certain number of crew. You need a licensed mate in addition to the captain. you must have a designated engineer onboard. You also need enough staff to perform night watch, regardless if the boat is underway or at anchor. The pilot had watch from 9:00-midnight, midnight to 3:30 AM, and 3:30 AM to 7:00 AM. Obviously the crew who did the night watches aren't very useful working on the dive deck the next morning or cleaning cabins the next morning, so enough staff is necessary to carry out the necessary duties while the night watchpeople slept.
Back when I crewed the boat (1995-2003) we would occasionally run with nine crew (a full crew was 12), but is was miserable. Imagine doing a 12-3:30 watch, only to be awakened at 7:00 AM to work on the dive deck until noon. We did it, but it sucked. Obviously tips were better with a smaller crew, but passenger safety and comfort should always trump crew tips.
Finally, the proof was in the pudding. Nekton ran with 12 crew for many years (at least from 1994-2001) and did very well. The boat was well maintained, it got great reviews, and customer service was top-notch. I still maintain it was the addition of the Rorqual that doomed the company.