SQL Server : how can I measure database performance increase after index maintenance?
You could use the RML utilities to capture a workload trace before and after the index rebuild and compare execution times.

RML utilities come with a reporter application that can compare the workload analysis of two trace files.

You can download it from here:

X64: http://download.microsoft.com/download/0/a/4/0a41538e-2d57-40ff-ae85-ec4459f7cdaa/RMLSetup_AMD64.msi

X86: http://download.microsoft.com/download/4/6/a/46a3217e-f523-4cc6-96e9-df73dd0fdd04/RMLSetup_X86.msi

The comparison will be more meaningful if the two workloads are comparable, even better if identical.