The event severity for failed object collection is way too high. It shouldn't be logged at ERROR level. Maybe WARNING at works, but preferably INFO. For example:

2015-03-19 18:29:07,481 ERROR [Collectd-Thread-32-of-50] o.o.n.c.HttpCollector: collect: http collection failed
org.opennms.netmgt.collectd.HttpCollector$HttpCollectorException: Unexpected exception caught during HTTP collection

Same goes for the JDBC collector.

It makes it difficult to find actually errors in collectd. It also deviates wildly from the somewhat related messaging in event severity for major, minor, warning (http://www.opennms.org/wiki/Event_Configuration_How-To#Severities). ERROR here would map to critical or major, which is not the case at all.