I guess it depends on what you find iffy about the ACR.
Since it's the Enhanced, I'll go out on a limb and say that the weight is an issue. If that's the case then you should look at a lighter handguard first, and looking at GunBroker you'd find better deals here. Other weight savings would require a solid commitment to the rifle.
You can also replace the trigger with most any Geissele AR-15 trigger. The only caveat is that you'll have to keep the ACR hammer spring since that is part of the safety selector mechanism.