What's the advantage of a gun like the Bushmaster ACR compared to a regular Bushmaster 223?  To me the ACR just seems more expensive without giving you all that much for the substantial price difference.

The more money you pay, the more awesome you get.

They are both different platforms. One is piston driven the other is direct impingement. (did I spell it right...... :) )

Anyways, is is up to you to decide what each has to offer and go for it. Folding stocks, barrel changes, other stuff....just gotta look at each rifle.

My useage does not offer any advantage to the ACR. The regular AR15 system is working fine.

Everyone's utility is different, but here's how I see it...

Myriad players in the market - Advantage AR-15
Widely available parts - Advantage AR-15
Competitive market driving innovation and keeping prices reasonable - Advantage AR-15
Healthy aftermarket support - Advantage AR-15
Proven design - Advantage AR-15
Quick change barrel - toss-up if you factor in some of the different uppers out there like the Hydra or the LMT otherwise Advantage ACR
Folding stock - Toss up if you consider the semi proprietary Para AR otherwise Advantage ACR
The newest thing out there - Advantage(?) ACR

Decide what's important to you.

That was a very useful answer.  Thank you!