Recently bought a technology card for only 30 SIM that I think makes a big difference. That is the Police Equipment card.
So what it does is that for every police station that you have, it decreases crime by an additional 1%. I have 7 police stations and had a crime rate of 16%. That's quite a lot, almost a crime every 6 days.
By spending only 30 SIM, the crime rate has been brought down to 9%. Quite a well spent 30 SIM and I'd recommend anyone else looking to bring down their crime to spend the 30 SIM rather than simply buying more police stations.
Now, if I can add a Neural Network card to the collection, crime rate should theoretically be brought down to 0. Unfortunately, these go for a lot more than 30 SIM. Anywhere in the range of 500 SIM to 1800 SIM. Hope to score one with the universities.