The simplest answer is that there is no interaction between the Super-Adaptoids. Common sense suggests that intent, but since serious rules parsing is more an exercise in logic than sensibility, perhaps someone can show me a clear misstep in or well founded support for my thought process.

What happens when a handful of Super-Adaptoids, including the M&M Unique, go to town with their special powers?

Super-Adaptoid (M&M) has these special powers:

ATTACK DRAIN: Give Super-Adaptoid a power action. As a free action it can use any standard or named attack power possessed by an opposing character 4 or fewer squares away to which it has a clear line of fire. Super-Adaptoid can use the power until it loses Attack Drain, Attack Drain is countered, or it uses Attack Drain to use a different power. After the resolution of an action in which Super-Adaptoid uses a power via Attack Drain roll 2d6. On a result of 2-5, deal 1 penetrating damage to Super-Adaptoid.

Based upon the bolded sections, it seems clear to me that only this Super-Adaptoid benefits from the power in any way. It is the one given the requisite power action to trigger this ability; it is the one possessing a power called Attack Drain, so it's use of a borrowed power triggers the roll in the damage clause. However, the final passage calls for Super-Adaptoid by name. This is not the likely intent, but I can see how one might make the case to injure all figures named Super-Adaptoid in this fashion.

DEFENSE DRAIN: When Super-Adaptoid is given a power action, as a free action it can use any standard or named defense power possessed by an opposing character 4 or fewer squares away to which it has a clear line of fire. Super-Adaptoid can use the power until it loses Defense Drain, Defense Drain is countered, or it uses Defense Drain to use a different power. After the resolution of an action in which Super-Adaptoid uses a power via Defense Drain roll 2d6. On a result of 2-5, deal 1 penetrating damage to Super-Adaptoid.

Defense Drain is slightly less clear-cut. Theoretically any power action taken by any Super-Adaptoid satisfies the exact wording to trigger Defense Drain. There might be some limited applications to this, such as copying Willpower when SA #1 uses Attack Drain, then switching to Impervious after SA #2 uses Running Shot. However, the second passage makes it clear only the SA possessing this power would benefit. And again there is language structure that might mean both take damage on a poor roll.

Super-Adaptoid (CA) has these special powers:

POWER TEMPLATE: At the beginning of your turn, choose a standard attack power that an opposing character within 3 squares can use. Super-Adaptoid can use that power until your next turn.

Here the language is a bit vaguer still, because no actions are called out. So long as the opposing character is within 3 squares of the Adaptoid actually possessing this power, one might interpret this to mean that any given figure named Super-Adaptoid benefits. This then raises the question of whether multiple CA Super-Adaptoids would use their abilities separately or share them. Perhaps the most useful application would be two SA's, one based by Winter Soldier, the other 2 squares away from Wolverine, both borrowing and sharing both BFC and RCE, the better to dispense with their respective targets.

ADAPTOID SPAWN: At the beginning of your turn, choose one: This turn, modify Super-Adaptoid's damage value by the number of friendly characters named Adaptoid within three squares; or, this turn, modify the damage values of friendly characters named Adaptoid by +1 if they are within 3 squares.

Adaptoid Spawn references 'characters named'. That's great. In addition to making this power fairly clear, it implies against Power Template being used as I described. It's very much in keeping with current wordings on powers, although that still results in some very unusual situations (like Larfleeze). But again we have the name Super-Adaptoid bandied about. Which Super-Adaptoid? Even if we presume it is the one actually possessing this power, what about when two copies are in play, one near more adaptoids than the other?

I'll confess that these questions came to me as I attempted (still in vain) to devise a credible force with the original Super-Adaptoid. Even if every SA's powers benefit all SA's, it still won't make him great, but it might make him a bit more fun. As it is... he stands on a shelf, mute in his sadness that he has such a cool sculpt and a dial to cry over.

That is not how powers work. Look at plenty of other powers and yu'll find many of them refer to the character by name. It applies only to the one given the action.

Again...the power only applies to that Super-Adaptoid.

Special powers do not work like that.

It is clear cut. A power only applies to the figure whose power it is unless otherwise specified.

Only ten minutes to catch your attention and get an emphatic response to a long post, Harpua? You must be restless today. Thanks for the input. As suggested, I wanted the answer to be a resounding no, but just felt that the combination of old rules wording with new rules wording might have created some unpleasant loophole.