Also, you can't monitor Eventlog with RPC, and you can't restart services if you are monitoring them with RPC. So there's a couple of trade-offs.
In our environment we really try to monitor with SNMP for the base stuff, and then go straight to WMI for the application monitoring. We've decided (for the moment) to monitor nodes with WMI (versus SNMP) only in cases where we need Windows Virtual Moutn Points or to get the IOPS calculations.