What makes the scepter unique compared to other weapons? That is probably a good start on thinking what to change to fix it.
Confusing images is like a slower greatsword auto with added confusion. Its damage per use is good, especially so with added confusion, but it might not be good dps. It is easy for the target and collateral damage to avoid. It is nice as a means to do some sustained damage in place of having to use the auto attack. A quarter or a fifth of your time can be spent channeling it. I doubt it will be made to do better dps so perhaps changing it to bouncing would fulfill a niche. Its aoe capabilities may be too high after that but it allows one more trait in the condition line to affect it. The hybrid damage characteristic would also be useful for tagging without worry of clones dying. Of course, if necessary, lower the amount of targets it hits. It rarely gets to hit 5 targets anyways.
The block is little more than a condition version of the off-hand sword, but it does pack a punch. Its effectiveness is a bit lacking in pve, but how much can we expect from a block in pve.
The unique thing about the auto attack is the clone creation. Adding direct damage makes it compete with a few other weapons and adding condition makes is a weak staff, as fitting as that may be. How about if the trait for the scepter was changed to support what the scepter does best? For example, add one more illusion to the cap. It fixes the phantom limit as a mesmer now ends up with 3 and a clone. It can work well with a shatter build, though it takes even longer to get the clones out. The illusion on-death traits will work a bit slower with replacements.
The other way the auto attack can go is faster clone generation for less dps. Make the auto look like an attack from the scepter clone to blend in better. Change the skills to give the option of auto attacking for fast clone spam or to use other attacks in place of the auto for damage. One option is changing confusing images into a dps excelling skill. A low cooldown skill that is channeled to replace time spent auto attacking for dps. The mesmer could have an option of channeling it for half the battle in place of auto attacking when the clones are not useful.
Confounding suggestions sounds powerful enough that making it better may be too much. There is always the option to change other traits to sell confounding suggestions as a grandmaster. What makes it unique is the stun. As I remember, that stun in fact overwrites the daze that procs it. It is an important distinction given what dazzling does. It also allows two interrupts when defiance blocks the effects. It is most notable in bountiful interruption. Perhaps the adept in the domination line can be changed to work like the master does when using stuns. A 50% chance for 10 vulnerability is an ok effect. Or wastrel’s punishment can have one bonus given for when the target is not using a skill, and another bonus for when the target is not moving.