What does the EU get in return for accepting Syrian refugees from Turkey?

It gets to fulfill its basic humanitarian duties in the time of war. This is far more important than any negative impact that might be created by an influx of refugees by way of dilution of cultural identity. There are always things to be learned from people of different cultures, and this interaction can also be used to identify with one's own culture more closely. Economic stimulus is also bound to occur when the workforce is buoyed by newer talents. The citizens will also find a way to get out and do more, learn more, travel more, inspired as they will be the work ethic of migrants, who will have more drive to build and succeed due to their uprootedness. All negative consequences can be addressed by a robust state organisation.