OP here again,
At the end we decided to go for it despite the recommendations from most ppl here. As you might have guessed we are not rich but we are still working so we can afford that little extra but we always go on the philiosphy of spending wise, especially after our previous experience on another cruiseline that concerige has no difference (and hence i asked the question)
Thanks for all those who have filled-in the info I did not know before. I also found a video of the Aquamar Spa Terrace on Vista so I know what it is like (small but has hot tubs, as someone said, it is weather dependent, I hope cruising in the MEDITERRANEAN during summer will give us sunny days)
I think the deciding factor really is the priority of getting the specialty dining. Last time we got a good deal to get on to the Regent 7 seas (as you might have guessed, we could only äfford" the cheapest catg) and as soon as reservations were opened for excursions and dining, it seems the best options were already gone, especially for those excursions that were most appealing (Regent advertised on their unlimited excursions, but they structured their half day excursions to be long enough that you could not get do two on each day, alas that is another topic) so it might be worthwhile to pay for a better chance to get the better time slots.
Again, thanks very much for all the responses, they were really helpful to get honest opinions.