If you have slavepits, and they are almost full, then yes, it's worth sacrificing the overkill amount of slaves.
But....the gain is not that big. With a normal raid or amazon-attack you'll get 1 slave every 10 units sent, with a maximum of 10% of the target's peasants. So to get 1000 slaves, you'll need to attack/raid someone with at least 10k peasants and something like 50k offense. When offense goes to 50k, then usually incomes are already above 100k/h. A bonus of 5k over 1200k every 12 hours.....it's not nothing, but I can't say it's a really significant amount.
Also, this is with the assumption of having full slavepits. That would mean that you have refilled your pits just before your attack, which is a bit a waste of spy-strength. With that spy-strength you might also have found a target with the same land but 400-500 defense less, which would result in losing 25-30 offense less, and thus saving 5k+ gold