A couple of thoughts...
* Years ago, when our church was young, we purchased a small church building on a small piece of property. Within 2 years, there was no more room. We knocked the walls out on the side of the auditorium (where classrooms had been) to gain a little more space, but ended up having two Sunday morning services simply to accommodate the growth. We had the same music, same message, same order of service, etc. We did this for about 2 years before recognizing that our two toilet building just could not accommodate 200+ people, even with double services. Shortly after, we purchased another church building and property which was large enough to handle our congregation size, as well as future growth. At that time we went back to single services. We truly did not feel that we were two congregations, but were temporarily having two services. Our most faithful members and dedicated laborers in the ministry voluntarily shifted to the early service for those 2 1/2 years, and our later service was primarily where our elderly, visitors and occasional attenders came.
* In our area, several churches have attempted the "two services, one church" format to accommodate contemporary vs. traditional services. None of these have worked. The churches that survive are those who make a choice in format and go with it... either contemporary or traditional or blended. When the services are intentionally different, then you create an "us" vs. "them" mentality. One service will become the dominant, and the other feel they are being slighted. Three churches in our immediate area switched to this format in the past 10 years, and all three have now closed. The 20 something kids were not able to support the church financially, and the older members fled with their checkbooks, and the result is fewer churches. It is sad.