I have had the same question for a long time. But I never found a way to monitor hits on an acl with snmp. As you said, it's very frustrating because the data is easily viewable on the CL.
Ultimately, I want to monitor how much traffic on a WAN link is VoIP traffic. If I could setup an acl to match the VoIP traffic, then I could count the hits.
Alternatively, I could monitor VoIP traffic when the routers see the different QoS values. But again, there doesn't seem to be a MIB for it.
Any tips or ideas for monitoring VoIP traffic are welcome.