I have done segments of a World Cruise and Grand Asia as well as a full Grand South America. I've also done segments on Cunard and Crystal (as well as a full Crystal WC). I think Holland America is the most egalitarian of the 3 in terms of what segmenters and full cruisers get. There are perhaps 2 things that segmenters will miss. Often, those on segments will only be able to get guarantees (they don't want those on the full cruise to need to change cabins mid-voyage); You should already have a status on that if you're booked. The other thing would be perhaps some hosted dinners.
In addition to having more events, more speakers, perhaps shuttles in some ports where a regular cruise wouldn't be one on a regular cruise there will be a "pillow gift" left from your steward each Gala night.
Those are the main things I can think of right now.