With regard to insurance, although in getting quotes we have been asked if we have an international driving license, it has never been a requirement.
IHMO an IDLicence is a scam. Only one company seems to provide it (IDL Service.com) at a cost somewhere over $100, by the time you have added this, that and packaging.
It appears to be only a translation of your driving licence into English, so that it can be read by US officials, and guess what? - Mine (UK) is written in English anyway!
More legitimate may be an ID Permit, available from specified Post office, over the counter, or by post for ?5.50, (plus a photo and current driving licence - check the website: http://www.theaa.com/motoring_advice/overseas/apply-for-an-idp-at-a-post-office.html). It does the same job, if you think you need one.
Though I do not have one, this may be a more useful item for people with the old style licence, as it combines a photo with your signature and may replace the DL so beloved of the US for identifying yourself, something which is becoming more and more common in US. It is even becoming common practice in some areas when buying gas!
The problem of not having an US DL with insurance is the lack of driving record, which adds a premium to any quote.
Acquiring a US DL is fun, but will only be valid for the time you are in the USA. As soon as you leave the US your temporary licence is invalid, so therefore your insurance would become invalid.
Incidently, however, even having an expired US DL seems acceptable to most places as ID.