Varese is hardly late 20th century!  You might try Christopher Rouse,
whose work I have found particularly appealing.  It has feeling, ideas
and noise when needed.  And the guy has a great sense of humor, as shown
in his "Der Gerettete Alberich," a kind of concerto for percussion which
imagines Alberich, the sole survivor of the Ring cycle wreaking havoc in
the orchestra.  I don't think it's been recorded as yet, but might be soon
by Evelyn Glennie.  I'd keep my eyes open.

Eric