What is the minmimum room size for Magnepan?

The 1.6's sound best at least 5 feet away from the rear wall and at least 2 feet from the side walls (preferably 3-4 feet). You should sit at least 10 feet away and 15 is about the right distance for me. All these distance vary of course per personal tastes but, you get the idea. I have 1.6's and the tweeters are fine and going on 2 years old. I do not know about them falling apart but, I have heard a little about the tweeter being fragile and my own tests have proved that wrong. I played an Innersound amp that had 1000 watts into four OHMS and you would not believe how loud those speakers get. I do not think you could damage them except with 'bad' power.

First, let me say I have extensive exprience with most models of Maggies in the last 5 years. I can say without a doubt, that there's no hard and fast placement measurement/distance rule(as with ANY speaker!) for the maggie!...it depends on the room, and the seating possition!(as with ALL speakers/set ups).
Really, this is a matter of knowing how to set up speakers in the first place..and most don't have a clue sadely. If you do it yourself, my suggestion is you, well, learn how to set up speakers in your(any)room. You'll have to play around with em quite a bit. Otherwise, hire someone such as myself, who knows what they're doing.
As for the ribbons durrability, well let' just say they "ain't" no rock and roll speakers....this is for certain. The ribbons are low efficiency/sensitivity designs, and will sound strained with heavy dynamic loads. In my oppinion, experiences, etc,you need to, yes, be carefull with the maggie ribbons, as they are the most delicate of speaker designs I think.
Good luck

In my experience as regards the durability question, the models you are asking about, which do not have the true ribbon tweeter, are rather impervious to overload damage. The panels will become distorted-sounding if you push the volume too high (easier on the MMG's), but just back off the power and they will be fine. But as always (and being especially careful on low-efficiency models such as Maggies, where the onset on amp distress can occur at lower volumes), do not let an underpowered amp deliver a clipped signal to the speakers! As for placement, let's just say look at other speakers if you have only a small room (especially for the 1.6's - the MMG's will work better in a smaller room, but as someone who doesn't believe in the concept of "small panels" to begin with, I would look at regular dynamic designs if the room is only big enough for those, because you will be able to do better than MMG's under those circumstances).

I believe most people think the tweeter/midrange panel is at their limit but in fact it is the power amplifier that is running out of power. Clearly this was the case when I had the Innersound amp like I mentioned in the above post. Even with my Plinius SA100 MKIII with about 175 watts of class A power (into 4OHMS) these speakers are not even close to playing as loud as they could go with the Innersound amp.

It is true that speaker placement in the room varies (of course) but, the point I was making if you really want the 1.6's to 'sing' you will want a big room. If they get too close to the back wall they become 'thick' and lose definition in the bass, if they are too close to the side walls they will get a blare in the midrange.

That is my experience and I know I do not have as much experience as some but I am very diligent in my accessments.