To solve this expression, we need to follow the order of operations (PEMDAS/BODMAS).

First, we calculate the exponents:
5⁵ = 5 * 5 * 5 * 5 * 5 = 3125
5⁷ = 5 * 5 * 5 * 5 * 5 * 5 * 5 = 78125
7⁰ = 1 (any number raised to the power of 0 is always 1)

Now, let's substitute these values back into the expression:
5⁵ ÷ 5⁷ + 12.3 + 7⁰ = 3125 ÷ 78125 + 12.3 + 1

Next, we perform the division:
3125 ÷ 78125 = 0.04

Now, we can simplify the expression further:
0.04 + 12.3 + 1 = 13.34

Therefore, the value of the expression 5⁵ ÷ 5⁷ + 12.3 + 7⁰ is 13.34.