In case someone reads this article in the future, SQL Server 2008 R2 on Windows Server 2008 R2 Enterprise (upgraded in-place) can and does use 64 GB RAM. Windows was patched last week and rebooted. 

After reboot:

    select counter_name, cntr_value<br>
    from master..sysperfinfo<br>
    where [object_name]='SQLServer:Buffer Manager'<br>
    and counter_name in ('Total pages','Target pages')


Result:

    counter_name      cntr_value<br>
    Total pages          7077888    <--54 GB
    Target pages         7077888    <--54 GB