I use nested stored procedures for the same reasons.
I quite often have
IF .....
INSERT #Tbl (Fields)
EXEC usp_SelectProc1 @Arg1, Arg2...Argn
ELSE
INSERT #Tbl (Fields)
EXEC usp_SelectProc2 @Arg1, Arg2...Argn
type routines.
The problem I have is that sometimes I want the usp_SelectProc stored procedures to use the INSERT/Exec method but you cannot nest this sort of functionality.
The comments I would make are that if you are going to nest stored procedures