If actually asking the question, the Inspire 3 will likely "be the platform" for a minimum of 5 yrs.
Waiting for an Inspire 4 will require technology not available or discovered yet.. the Inspire 3 provides technology useable for years that the Inspire 2 lacks and greatly improve the Inspire platform.
Me, not an income source... serious hobby. I'll entertain an Inspire 3 a few years down the road when some are selling used.