Step 1: Total numbers possible.
We are arranging 4 digits (1, 2, 3, 4) to form 4-digit numbers. The total possible numbers:
\[
4! = 24
\]
Step 2: Contribution of each digit.
Each digit appears equally in each place value (thousands, hundreds, tens, ones).
So, in each place:
\[
\frac{24}{4} = 6 \text{ times each digit.}
\]
Step 3: Sum of digits.
The sum of the digits is:
\[
1 + 2 + 3 + 4 = 10
\]
Step 4: Place value contributions.
Each place value sum = \( 6 \times 10 = 60 \).
Thus, the total contribution =
\[
60 \times (1000 + 100 + 10 + 1) = 60 \times 1111 = 66,660
\]
Step 5: Multiply by number of sets.
We already accounted for all 24 numbers, so total sum =
\[
66,660 \times 24 = 711,040
\]
Final Answer:
\[
\boxed{711,040}
\]