If we can predict into the future, why just bikes? An estimate of future value for a collectible, commodity, or business is based on a combination of knowledge and experience.

Did anybody ever expect the following:
Muscle cars of the 1960's to be worth 10X or more of original value?
Gasoline prices in the USA would plunge to $1.75 or less in January 2015?
Apple Computer worth > $700 billion?
NFL Buffalo Bills would sell for $1.3 billion last year?

On a used bicycle or collectable, location, condition, provenance, buyer's intention/attachment mean everything.