adjectives - Agreement With Compound Subjects Joined by And

I was surfing the internet the other day when I found this phrase:
Instead your precious time and attention is wasted.
To my ears, it sounds wrong. But I'm not a native English speaker, so I consulted with a number of them, and some of them said that it was "is" because the adjective modifies only the noun "time" and not "attention". Others said it "is" because that's just how it is.
But I still believe it should be "are". Any help is appreciated.

Answer

The claim about the influence of the adjective is misleading – the major question is whether time and attention are separate concepts or time and attention is a single composite concept. See at http://grammar.about.com/od/rs/g/Subject-Verb-Agreement.htm (under
'Agreement With Compound Subjects Joined by And')

Consider:

Bacon and eggs is my favourite breakfast.

Bacon and eggs are both a lot more expensive than they were 40 years
ago.

Usually, there is a virtually idiomatic status with 'apparently plural assemblages treated as singular':

Bangers and mash, also known as sausages and mash, is a traditional
British dish...

Fish and chips is a take-away food...

Research and development is of great importance in business...

We believe that good health and safety is important...

(all Google)

There are relevant hits for "time and attention is...":

Or is it because so much time and attention is given to the latter

but also for "time and attention are":

But equally important is the nature of the instruction to which student time and attention are devoted.

Time and attention are equally important in the consumer market

The concepts are inter-related and thus may be considered as a whole, but the words do not really constitute a fixed expression, and so may also be considered individually within the phrase.