So 'have a keen eye for' accepts count nouns. 'Have a keen eye for a bargain' is an idiom within an idiom and apparently count. Have a keen eye for detail is a longer set expression, and obviously uses the non-count version of 'detail'. However, this does nor indicate that 'have a keen eye for details' is in any way wrong. More @Wikipedia
Get the latest news about Blink Of An Eye from the top news sites, aggregators and blogs. Also included are videos, photos, and websites related to Blink Of An Eye.
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.