First, just to emphasize the premise, there are 1250 staterooms on the Dream and Fantasy and 40 of those are concierge. That means roughly 96.8% of the passengers on each cruise do not have access to concierge. Concierge on
DCL is a very exclusive form of travel that unfortunately is beyond the budget of most families.
I chose concierge for our most recent cruise after opting for regular rooms for our first two. We were a party of 9 and shared rooms 12004 (concierge stateroom) and 12012 (1-bedroom suite) on the Fantasy. My main reason for justifying the extra cost was that we were 3 generations together and I wanted more private room for grandparents, some with mobility issues, and grandchildren to be together. During our first two cruises, we spent almost no time in the staterooms. Instead, we were constantly splitting up and moving around the ship: some doing the AquaDuct while others were in the pool or in the theatre watching a movie etc. That worked perfectly for parents with children and we all had a blast. But, with a larger party including the grandparents, I felt that paying twice the price was worth it.
The concierge cruise ended up very different from our previous ones. We spent the vast majority of the time together, either in the lounge, the suite (in particular the extra large verandah that comes with 12012), or the sundeck (which the family curiously loved, we hardly saw another guest up there the entire cruise). I've never seen my extended family talk and interact as much as we did this week. I had hoped it would work that way, but it far exceeded my expectations. When someone went somewhere else on the ship, it would be to do something very specific and they would then come back and join the rest of us. Another thing, we absolutely loved, was to bail out of the MDR dinners early and have dessert up in the lounge where we'd put 3 tables together and sit, everyone together, and talk. It was _so_ much nicer and quieter.
To answer the question of the OP, I would definitely have said that I could go back to a regular DCL cruise before trying concierge, but I find it much harder to answer after I actually did. I've noticed that prices are going up significantly for concierge and an equivalent cruise next year would be 15-20%. The more prevalent question for me is "if I don't want to pay for DCL concierge, what is the best alternative with another cruise line"?