Aphids are easy. Mix crushed chilli, vinegar, dilute with water and spray those little fuckers.
If you feel particularly nasty, add a little soap to the mix and you'll see them drop off in pain in real-time as you spray.
It's true that his innovations and inventions will help increase yield and production all over, but the real treasure lie in the town's people. The idea of having so many well-trained, intelligent people means they're in a position to implement and exploit those innovations and inventions. You give the same winnower to a regular peasant and they wont know how to improve on it or maintain it if they've relied on traditional methods all of their lives. Or crop rotation is not going to take off if people are not smart enough to see the benefit, let alone growing monocultures in fields since poor uneducated people will not want to lose their land to grow their own produce, etc. Having smart, educated people that are able to see the value and employ/improve on it is key. That's what the king wants more.