Here's an excerpt from a recent article about PCGS:
"Since its founding in 1986, PCGS has certified the authenticity and grade of over 16 million coins with a total value of more than $18 billion. The popular PCGS Set RegistrySM program has over 36,500 U.S. and world coins sets registered by collectors and dealers."
When you add up what the other certification services have done, plus ungraded coins (including uncirculated numismatic/collector coins), its easy to estimate that the value of all coins held by collectors is in the $40 to $50 billion US dollars (or more). Is there another hobby anywhere that exceeds this amount?