High channel utilization can have a lot of reasons, most of the times high channel utilization is being seen on the 2.4GHz due to the limited (non overlapping) channels and the fact that 2.4Ghz reaches about 2 times further than 5GHz signals do. But there are a few thing we can do to make the best of it.
First of all what is your definition of "high"? If you look at the channel utilization of one of the access-point radios you will also see a "radio RX" and "radio TX" value. Those values show how much channel utilization that access-point radio is responsible for. When those values are low but the channel utilization is still much higher you run into something called co-channel interference (CCI). This basically means that other access-points in the neighborhood are using the same channel.
Now, if those other access-points are yours we can do the following things to make things better:
Disable lower data-rates so clients will try to roam earlier
Use directional-antennas instead of omni
Try to use as less SSID's as possible ( Maximum 3 is the recommendation)
You need to do a site survey before and after doing one of these things, if you really want to know the outcome. Use with caution.
You have these nice high-end MR56s you paid lots of money for. You probably have lots of nice notebooks. You spent all this money on the network and machines - and then retard it by allowing 2.4Ghz to be used.
It is better to replace a small number of 2.4Ghz devices, than risk affecting the performance of everything else.
Agree that disabling 2.4 is a much better approach if you can support it. I made this leap 2-3 years ago after getting fed up with users reporting issues. Occasionally someone comes with a phone that doesn't support 5Ghz but its just the way it is.
Surprisingly a lot of Samsung phones even mid range devices didn't have 5Ghz. No idea if thats changed or not.