Network management is hard. It's a part of the design that the effort is front-loaded: if you plan ahead and organize what gets monitored and collected according to rules, then the effort involved in adding nodes down the road approaches zero. It's an approach that doesn't make sense for everybody's environment, and you should absolutely use what works for you. All kinds of people find that OpenNMS works for them; a few who have written up their stories are listed here:
http://www.opennms.org/wiki/OBP
As for having somebody "to yell at", The OpenNMS Group sponsors the project and provides support, consulting, training, and custom development for OpenNMS; check opennms.com for details (disclosure: I'm an employee). We make two promises about OpenNMS:
1. It will never suck
2. It will always be Free (as in Freedom)
