On a properly written server you could "fuzz" the date of "if-none-match". Then it would still work for caching, but would not uniquely identify you.
The trouble is that most servers are not written properly, the date is not parsed, rather it's string compared with the file date.
For example if the server sends the timezone as EST vs +0400 the browser will send it back exactly as it gets it, when normally you would think that should not matter.
Would hurt the server a little and reduce speed because there would not be any caching but still helps guarantee no tracking.