Countifs(..) works as a set of AND statements, not OR statments - e.g. if you had Surname/Forename/Gender, the code =COUNTIF(A:A,"Smith",C:C,"Female")
would count Females in the Smith family. (You also have to specify each column separately)
The two solutions I can supply are A) have a macro to apply a TRIM to every cell in the intersect of UsedRange and Columnd IG to that all the spaces at the start/end vanish (and then possible clear the cell if LEN is 0?) or B) Use COUNTA to get non-blank and then subtract the other conditions:
Dim tape AS Worksheet, out As Worksheet, rTEMP as Range
Set tape = ThisWorkbook.Sheets("Agg")
Set out = ThisWorkbook.Sheets("output")
Set rTEMP = tape.Range("IG1:IG10000") 'Any specific reason for not just using the whole column IG:IG?
out.Cells(1, 2).Value = WorksheetFunction.CountA(rTEMP) - (WorksheetFunction.CountIfs(rTEMP,"<>",rTEMP,"""")+WorksheetFunction.CountIf(rTEMP," ")+WorksheetFunction.CountIf(rTEMP," ")) 'count of Non-blank cells minus the sum of counts for Non-blank 0-length, non-blank 1-space and non-blank 2-spaces
Set rTEMP = Nothing
(Checking for a non-blank 0-length cell is an extra special case, hence it uses CountIf)