Where do you draw the line on hiring a "rigger"? ... EC may choose to use rigger but I don't think those tasks and many others are outside what might be expected from an EC either.
Setting light poles is EC or rigger job? << If the EC has the bucket/crane truck to set the poles, go for it. Who pours the foundation and sets the anchor bolts?
Running 4" RMC at a 30 foot ceiling - EC or rigger job? << EC-- with a pair of scissor lifts, one at each end of the pipe.
Hanging large luminaire - EC or rigger job? << EC-- with a scissor lift; probably 2 guys up there.
Setting a large switchboard or MCC in place? << EC-- but who drives the fork lift? Don't you have to be 'licensed' to drive one in most plants?
Company I worked for had a fireproof safe/vault to be installed, and later, moved. It's about 6' wide, 7' tall, and 4' deep. Weighs the proverbial ton. It was definitely a 'rigger' job!
When the OP mentioned several 500# displays, I imagined they were electronic display panels, like one of those signboard complexes dangling overhead at the airport-- 3 or 4 screens around a central mount. As someone asked-- how strong is the ceiling?
I think the decision has to be based on the EC doing the job-- what are their skills, equipment, training, etc. Not every EC has the right mix to do every job.