I have tried the following: (join.pl is Corion's script)

C:\scripts>perl join.pl --null "--" --left 1,2,3 --right 1,2,3 --delim
+iter " " --missing 1 --missing 2 file1.txt file2.txt > file12.txt

C:\scripts>perl join.pl --null "--" --left 1,2,3 --right 1,2,3 --delim
+iter " " --missing 1 --missing 2 file12.txt file3.txt
ID NAME date Val1 Val2 Val3 Val4 Val101 Val102 Val103 Val104 Val101 Va
+l102 Val103 Val104
1 ABC 04-05-2013 10 11 12 13 50 51 52 53 -- -- -- --
2 XYZ 04-05-2013 21 22 23 24 -- -- -- -- -- -- -- --
1 ABC 05-05-2013 30 31 32 33 -- -- -- -- 60 61 62 63
2 XYZ 05-05-2013 41 42 43 44 -- -- -- -- 71 72 73 74
[download]

So nearly there...