I've never used one but I can say that since using the Silhouette SD and perfs, I'm sold on the concept. Basically a perf would work/does work, just as well.

how many 'cuts per inch' does the Silhouette SD make when it creates its perf.lines ?

There is a tool called Cutter Bee Bugs Perforator that has a retractable wheel that perforates paper. It is used mainly to make perforations for ease in separating parts, but looks like it could be modified some what for scoring/folding. You can find it in a multipack that also has a Cutter and Scorer (the Scorer does not cut the page, it forms a shallow indentation like when an empty ballpoint pen or some other blunt object is used). You can also find it without the other two. Price for the Perforator is somewhere around $4.00 US, higher or lower depending on where you buy it. You can find it online or in some craft stores or in stores with a crafting section.

It looks like it makes 11 perforations/inch. The modification needed would be to increase the gap between the perforations by narrowing the cutting blades.

Here is a closeup of the wheel and perforations:


Here is what the tool looks like: