I welcome anyone to add to this, but here is a start of some suggestions to help make the material converter better.
Old conversion of material. Note this material had a fresnel in the reflection.
Here is what it would look like with my suggetions. Changes are as follows. The Mix Shader was replaced with an Add Shader as the reflection is always added on top of the diffuse in C4D.
A Fresnel node was added to the Color of the Reflection as the original had fresnel on the reflection. This Fresnel value should be taken from the Fresnel value in C4D. I'd also suggest 2 HSV nodes connected to each other, as shown below, so the Value could be set on one to the value of the layer strength and the other HSV Value set to the Reflection Strength. If there is more then one Layer for reflection in C4D a Mix node should be used to get more then one reflection mixing so it looks the same as it would in C4D.
A Hue Saturation Value node was added between the Alpha input and the texture being used for the Alpha because in most cases people will probably want to tweek it.
Another one not shown here is if Additive is checked under the Transparency an Add Shader should be used as a node between the Refraction and any other channels instead of a Mix node.
A C4D Transparency will put a reflection in the relection layer for the reflection of the Transparency so it will by default look like glass. This Transparency relection has fresnel and can't be deleted in C4D. Even turning off the Reflection layer won't turn it off. The only way to turn it off is to uncheck the eye next to the "* Transparency *" layer in the Reflection channel. The conversion of materials from C4D to Cycles should reflect all this.
The should also be a Add node between a Refraction and Gloss node in Cycles when a Transparent mat is converted from C4D.
I've got a ton of other things I could suggest to make the material converter wayyyy better. It would take me many hours to make the list and show examples. These are the things that are the biggest headaches.
As a further note the materials in the Starter Pack are abysmal. I'd completely take that off the marketplace because it confuses a lot of people starting off with cycles making them think that is the way materials have to be in Cycles. All the materials are way over complicated and others are just plan wrong. I'd be willing to spend time finishing this list to make a great material converter and/or make a good starter material set if you like give me a PM or email.