There are definitely scientific (political science) and policy papers out there.
In 1998, this article by the Inter-American Development Bank found that decentralized governments were typically larger. They propose two reasons:
1.) In a decentralized government, budgets are soft limits. A sub-national unit (state, city, etc.) can always ask to be bailed out by the national government. In this sense, a decentralized government has the ability to expand more than a centralized one.
2.) In a decentralized government, many agencies may tap the same common resources. A single, centralized government would use less of the resource because it can ration it's usage, but multiple agencies will probably not coordinate.
Several state legislative auditors in America, as well as the GAO routinely investigate service overlap.
On the academic side, results are mixed. Some research shows that decentralized governments are typically larger because of service overlap/duplication (many agencies providing the same service). Other research finds that decentralized governments are smaller because departments can specialize (the federal Department of Education doesn't have to worry about the details of schools in a particular state, because the state Dep. of Education handles tha).