We have sailed in the category you are inquiring about 2 times with our young boys (5 and 7 now) on the Fantasy and once in a one bedroom on the Dream. We have sailed 6 other times in regular verandah staterooms, one of those times with kids, (the rest of the cruises were pre kiddos!) Having that comparison, I think concierge is worth it. It simply makes sailing with kiddos much easier and the concierge staff will go out of their way to ensure you and your family have anything and everything you need for your cruise. If you have a son that needs some more quiet time more than others, the lounge is a blessing. Our son worked on homework in the lounge, we would grab a quick and easy breakfast in the lounge, and for mom and dad, the espresso machine and cocktail hour can not be beat! They have a private character meeting for concierge guests only, which is geared for the little ones (and adults too...lets be honest...). Having the lounge allowed us to have some nice settle down time without having to always head back to our room to have it. If getting specific reservations are important to you, sailing concierge is the way to guarantee what you want.
I will also say that we are not first class flyers or 5 star hotel stayers. Sailing concierge means more saving on our end and we make sure to save money in other areas (bringing our own alcohol on board, sailing in off season, etc). But we have found it makes our sailing experience with our, shall we say, "lively" boys easier and more enjoyable. Now, that being said, now that our boys are getting to the age when taking them out of school is harder and more stressful for them, we probably won't be able to afford the concierge rooms in peak season....and we will know we will have a great time without those extra services, but we will swing it as long as we can. If you can, it is worth it, IMHO.