Benefits of C# Com Interop vs VB6+IDL

Strictly from a COM Interop point of view (ignoring other benefits C# might bring), are there any benefits of:

1. using C# .NET (via System.Runtime.InteropServices), vs


2. using an IDL to maintain a Type Library for VB6

in order to manage (control GUIDs, maintain compatibility, etc.) a COM+ Interface? Does InteropServices provide anything that isn't possible with a IDL, and vice versa?

For example, I manage an ActiveX DLL developed purely in VB6 that is consumed via a COM Reference in Excel. This DLL currently does not use IDL/TLB to manage the Interface and relies on Binary Compatibility. If a developer was to choose from the above two options to take control of the COM Interface, is switching to C# enough of a benefit to warrant a 100% software rewrite or would IDL-maintained Type Libraries for VB6 provide the same results with less rewrite work?