How do I convince my users not to use a sketch UI?

Question

I recently worked on a prototype of a new system using Sketchflow, and now some key stakeholders are pushing for a sketched look & feel in the final product. To make matters worse, the people viewing the prototype were asked to provide feedback on the sketched look & feel by way of a fairly leading survey question, to which 80% of the responses were positive.

It's for an enterprise application that will mostly be for internal clients, but is also intended to be used by some external clients.

The main reasons I have for it thinking it's a bad idea are:

• It doesn't look polished or professional
• The significant effort involved in skinning an actual application in the sketched style
• The sketched style doesn't make efficient use of screen real-estate

I've been trying to figure out what the appeal could possibly be, and the only thing I can come up with is that people are attracted to the simplicity of it -- especially when compared with the existing system(s) it will be replacing.

Can anyone point me in the direction of evidence of why using a sketch look & feel is a bad idea? Ideally something based on UI research. I'm worried that my voice isn't going to be listened to unless I can point to something concrete.

[Edit]

I should probably add that the difficulty of skinning the application is compounded by the fact that it is intended to be delivered as one or more Silverlight webparts in a Sharepoint site. Getting a consistent sketched look & feel across both technologies could be very difficult.

[Edit]

Just in case anyone's not sure about what a Sketchflow prototype looks like (and therefore what the people in question are asking for) they're essentially asking for a production application to have a pencil-sketch wireframe look & feel.