Well let's look at it this way:
With concierge, you will get many food offerings throughout the day from breakfast to late night snacks. The concierge building (Hawaii) also has a lounge that offers a GREAT view of the MK and fireworks. (I haven't stayed concierge, but I did walk by the Hawaii building many times).
A Lagoon view room would give some the BEST views of the MK on property. You could site on your balcony or patio and watch the fireworks, see the sunrise or sunset and be able to see the castle, the Contemporary and the Grand Floridian. (All beautiful things to look at if you ask me!)
So, you have to decide if you want food, AND if you'll be around to ENJOY the food, or do you want the view? All the rooms are basically the same size. I'd actually recommend the Tahiti building for a lagoon view room. There are balconies on both the 2nd and 3rd floors, there are double sinks in the bathrooms (Hawaii only has one sink) and the Tahiti buidling is a bit newer than some of the others. Plus you're closest to the TTC where you can hop the monorail to Epcot. You're not that far from the GCH either, where all the Polynesian's restuarants and shops are.
In my opinion, I'd rather have the view because I enjoy the Disney restaurants more than I think I'd enjoy hanging at the hotel just to eat from the concierge lounge. Again this is just my opinion. If you have a family, however, it may be more cost effective to go with concierge because then you're not spending tons of $$$ on food for the kids.
Hope this wasn't too long and I hope I helped answer some of your questions!