I would do that this way:
SELECT SUM(CASE WHEN APPD_NEXTREPLDATE IS NOT NULL THEN 1 ELSE 0 END) AS pastDueRepl,
SUM(CASE WHEN APPD_NEXTINSPDATE IS NOT NULL THEN 1 ELSE 0 END) AS pastDueInsp
WHERE APPV_PTSSTATUS = '2' AND APPD_NEXTINSPDATE between DATEADD(Day,-30,GETDATE()) and GETDATE()
Note: it should be much quicker then method provided in solution 1, because a dataset is filtered only once.