They value the Harrier and it's unique capabilities. The super hornet is restricted to carrier and finished runway operations.
It may be a go fast airplane but it doesn't meet the needs of the USMC when it comes to organic close air support.
Unfortunately the Super Hornet, and Hornets in general, are some of the slowest fighters around. I do think the USMC should have some of their legacy Hornets replaced with Super Hornets. They have some of the oldest Hornets and procurement rates of the JSF are going too low to give them what they need. Even a few squadrons that would be eventually transferred to the Navy would be a good idea to keep up their combat readiness.
The obvious priority will be to get rid of the Harrier. It has been a disaster of a program.