Adjective/adverb that means "seemingly clever, but actually foolish"
If somebody says things that seem sensible, but are actually foolish or wrong, you can call their words specious.
I realise this is too late to help the original poster, but there is another great word with a similar meaning: Meretricious: seeming good but no so, or 'apparently attractive but having no real value'. This word is often used in the phrase 'a meretricious argument'. It is used a lot by Harvard economist John Kenneth Galbraith in his book The Affluent Society to mean exactly what the OP suggested. Etymologically it is interesting coming apparently from the Latin word for prostitute.
Among single words for "someone... clever or smart on the surface, but... actually quite foolish or unproductive" is wiseacre, "One who feigns knowledge or cleverness; an insolent upstart." Some related terms: smart aleck and cleverclogs, the latter meaning "An intellectual who is ostentatiously and irritatingly knowledgeable". [edit: I now see clever-clogs got mentioned in an earlier comment.]
Another term to consider is Trojan horse, of which Wikipedia notes:
Metaphorically a "Trojan Horse" has come to mean any trick or stratagem that causes a target to invite a foe into a securely protected bastion or space.
Good question. Another approximation might be sciolism, which is defined as superficial or pretentious knowledgeability.
See also: Sophistry
- a. a method of argument that is seemingly plausible though actually invalid and misleading b. the art of using such arguments
- subtle but unsound or fallacious reasoning
- an instance of this; sophism