Don't understand the question, really.  I suppose constructivist might bridge the unit/system gap.  Barker has, among others, written on constructivist realism.

I guess the circumstance has not changed substantially, the debate between the two main arms of IR remain perennial, regardless of the effort of the social constructivist school of thought. Alexander Wendt's ideas though appears outstanding, but our world remains dominated by the mantra of rationalist (power politics) and that is true for all unfolding belligerent realities, shaping global affairs.

I don't think power and rationalism have to be in the same breath.  If one has power to build--the most complex kind of power--then it likely involves considerable collaboration with others and at least accommodation of interests.  I'm not saying the Post WWII institutions built by the US and Europeans did involve the interests of other powers, much less people still under colonial rules (internaitonal law largely developed to justify colonialism).  There are irrational uses of power of the violent and financial kind, to observe, too.

There is a need to redefine Power as per the current status of the Realist Perspective.  

Yes I concur with the view shared by Palak that the notion of power need redefinition. The traditional concept of power has changed over the ages and in my humbly understanding, the constructivist narratives support this notion. State-centric power definition of international relations is out of place, power has been relocated in a number of ways and directions. Meanwhile, different form of explanations are used for the perpetuation of these kinds of power exhibition. Yet, Mary's view is no less a starting point for further discussion of the relations between the rationalist and structuralist.    

Thank you all for your comments. Indeed power is one of the key elements of realism and also of a Foucauldian poststructuralism. [For example, A.J. Paolini has written about power and IR theory: "Foucault, realism and the power discourse in international relations". But I have no access to this paper.]

The tension I see between structural realism and rationalism is that structures (co)constitute the actor, whereas in rationalism (in a rationalist world) one would assume that the actors could (structurally, qualitatively) change the structures they are in.