Russia has ... three sources of weakness, inherent and irremediable--Poland, the Caucasus, and the Fleet. All these deprive her of immense sums of money and large masses of men.
So what about those three sources of weakness today?
The fleet surely hurts. I've mentioned more than once that for such a large country, building a fleet capable of fighting for control of the oceans is foolish.
And Russia has fought three wars in the Caucasus (two against the Chechens--that is still kind of active, really; and one against Georgia) since the fall of the Soviet Union; and must deal with terrorism coming from Moslem subjects there who don't like being controlled by Russia.
The Poland comment is interesting even though Russia doesn't control Poland as it did when the comment was made nearly two centuries ago (and as it did during the Cold War). So Russia doesn't have to devote money and masses of men to control Poland--from the Poles or from a modern Western European state that might contest Russian control of Poland.
But with Russia determined to pose as the enemy of NATO, Russia would need to build an army capable of advancing through Poland to the German border to pose a real threat to NATO (and link up with Russia's Kaliningrad exclave).
So if Russia builds an army (and air force) capable of driving all that distance, Russia will indeed have to spend immense sums of money and gather large masses of men.
So Lord Durham is still right, it seems.