It depends what question you are asking. If the question is "should we fund projects even if we don't know if or when they will have demonstrable results?" then I would argue that, yes, some portion of research should go towards that.

How long is "long enough" to deem that a line of experimentation "didn't work out?" There is no period long enough. Sometimes a negative result is quite useful down the road. Some research just comes together when the right things are learned and tried. So any notion of a "dead end" is really just a tentative assessment, frozen in time.