Are you asking if negative interest rates will be good for "hard assets"?  I think that depends on what you mean by hard assets.  Certainly, a trend toward ever lower interest rates means improving gold and silver prices, being that they are hedges against depreciating currency values (in the present situation). 

As platinum group metals have higher associations with industrial applications (like copper, zinc, moly, etc.), they are not likely to perform well by comparison.  So, metals and mining, in general, will not be a good bet, important discoveries excepted.