Man, Sue raising those shields and walls are epic!
Really liked the differences between characters on the flying levels. Sue shielding the vehicle, Torch flying freely, etc. I would recommend you give Torch a dash forward and maybe Mr Fantastic could make better use of his ship (like firing a bigger laser, like his special, but horizontally). Thing would be the least effective "flyer" (though IIRC, he is the team's pilot... so maybe he could be faster with the ship, or have a "dodge" up/down). Well, a lot of trouble for such small improvements.
Regarding the helpers, I think if you would add more, either make them appear only when there are no radios, or maybe just make them radio helpers. About Dazzler, maybe you could make her Cyclops helper (she had a thing for him on the cartoon, didn't she?) - btw, he could summon two or more helpers, since he is the x-men's leader.
What you also could do is have "event" helpers: on some predetermined parts of a stage, a helper would appear and make an attack (or action) and quickly move away. Cloak teleports Dagger in who shoots light and teleport out (like on Maximum Carnage), Scarlet Witch flies in and turn enemies to stone/toads/boxes, Dr. Strange casts a spell to teleport enemies away, Professor X's astral projection appears and confound enemies (Jean's mind control effect), the Blob drops himself over an obstacle to clear the path, a SHIELD helicopter comes down and shoots everyone... Well, also a lot of trouble for small improvements (and esn is right, you already have too many characters!)