Yes, "worth" is an adjective (or prepositon), so you need the verb "are" to make a sentence.
This is, however, a motto, and not a complete sentence, but just a noun phrase like:
"Ideads (which are) worth spreading" or "Ideas (being) worth spreading."
gainni21's "Ideas worth spreading" = wind-sky-wind's first proposal, "ideas (which are) worth spreading.", and would be found in a context like "These are ideas worth spreading."; they are ideas which are worthy of being spread/which deserve to be spread.