I have a Silhouette SD right now, and intend to get a Silhouette Cameo in the next few weeks, and I can tell you with no reservations that it is an INCREDIBLE product.
The software takes a little getting used to, but if you can do work in GIMP/Photoshop, then the Silhouette Studio program isn't much of a learning curve. It's mostly little quirks that you have to just get used to doing it how it was set up.
As for the fineness of the cuts, it's intended for 80lb stock and under, but I have cut 110lb card stock many times in it, albeit at "10" blade length (on the adjustable blade), highest pressure setting (default for card stock anyway), and selecting 'double cut', which re-traces the paths it cuts to ensure they release completely.
The laying out of lines to cut can be tedious, no doubt about it, but being able to do things like tank tread links for instance is profoundly helpful with the Silhouette cutter. I merely need to trace one, and since they are all uniform, I can select, copy, and paste the pattern over the rest in a "row". Then since the rows are of course the same, I can copy/paste an entire page of cutting lines in a matter of minutes, print it out, and set the Silhouette to cutting.
In 5 minutes it can cut far more accurately, cleanly, and uniformly than I ever could in hours, and the project is easily saved in case I need to do a reprint and replace a botched part or just do a project another time. The time used in outlining projects or tracing a cutting path is more than saved in hand-cutting each tiny piece of some projects and of course the lack of hand cramps are a welcomed benefit.
If you're averse to doing a little tedious work on some tracing, then you've likely chosen the wrong hobby to begin with... Paper modeling isn't likely to be on ESPN anytime soon after all.
I can't begin to praise the Silhouette cutter enough, and while I'm not going to retire my Silhouette SD cutter anytime soon, I definitely want the Cameo for its 12" x 12" cutting area (it can also cut up to 12x24). The smaller Silhouette SD cutter is somewhat limited in width at a bit less than a standard 8.5" Letter-size paper width, so some projects may have to be confined by those limitations, where as the Cameo can readily cut A3 size paper (11.69 × 16.54) if you have the right mat and settings (they offer a 12"x24" cutting mat).
Either model is definitely an investment, and not for everyone, but for cutting repetitive parts it's worth is beyond description. The machine never gets tired, and never gets impatient. If it does mess up, it's merely a reprint away from being fixed. Best of all, its speed even on the slowest setting (used for thick card stock) is still many many many times faster than any human could cut the things out with accuracy, especially on curved parts and interior corner or curved cuts that would be otherwise hard to do even with an exacto knife.