Do we give undue to importance to grammar teaching? is incorrect - it should be just 'undue importance' (with no intervening 'to').
The Macmillan ED has a pretty good breakdown of the items concerned:
http://www.macmillandictionary.com/dict ... tish/undue - "
ADJECTIVE [ONLY BEFORE NOUN]..." (i.e. with no intervening 'to'), meaning "not necessary or reasonable" (also, "excessive, too much")
http://www.macmillandictionary.com/dict ... ritish/due - note senses 1 and 2 are "
NEVER BEFORE NOUN" (i.e. that prepositions or particles intervene between the 'due' and whatever follows it). Sense 3 essentially means "sufficient, enough" (cf. the "excessive, too much" above). Sense 4 is clearly predicative rather than attributive.
http://www.macmillandictionary.com/dict ... ish/due-to# (a [multi-word] preposition rather than an adjective. A one-word rough equivalent, though it won't sound as natural in most contexts, is 'from')
Lastly, have a search for the string "undue to" on Google (double quote marks produce results for that exact string). I found the following meanings in just the first couple of pages of results:
"Nothing undue (=untoward) to report"
"Undue (apparently a racehorse's name) to follow Oakleigh winning formula"
"Cuba: net access limits undue (=not due) to politics"
"Now divine honor is undue (=not due) to idols"
"He called on the minister, to exert the whole of his influence, due or undue, to stop this Bill, quoting, 'Flectere si uequeo..."
and so on.
