There are a couple different ways to get fine details like these. The most obvious is to add geometry and model in the details, which is what it sounds like you're trying to do.

Unfortunately, I'm having trouble understanding the exact nature of the scaling problem you're having. When I extrude and scale on the file you uploaded, everything behaves pretty much as I expect it to. If you can provide more details about the problem you're experiencing maybe somebody can offer more insight, but some things to try:

• try "scale along normals" (alt-s) instead of scaling (s). I use "scale along normals" a LOT when modeling

• try extruding in different modes (face/edge/vertex). I find that extruding in face mode is often what I need when trying to "pull out" volume from a surface detail like buttons, buckles, etc. rather than in extruding in vertex mode

• Try modeling the details as a separate object in its own object space that simply overlaps or intersects with the main object, and then join the objects later when you're happy with the position of the detail.

You can also use normal and displacement maps to add details as was mentioned. There are plenty of alpha images out there for textures like stitches, and throwing together stitching or other details in photoshop or GIMP isn't terribly hard. Once you have the details in a texture, you just map them to the displacement or normal influence (using "Normal" or "Displace" under the "Geometry" section) instead of mapping them to diffuse color. This can give the appearance you want in your final render without increasing the model's vertex count.

As somebody else in the thread mentioned, you can't use normal maps in Cycles, but you can bake the results of a normal map into a displacement map and use that instead. There are differences in displacement and normal maps, but the majority of the times, the results are similar enough that you can make it work.

There's another way to use normal maps with Cycles: a displace modifier using "Normal" for the Direction, combined with either a subsurf or multiresolution modifier. 

A third option for these details is to use Sculpt mode with a multiresolution modifier. You can sculpt in the details either freehand, or using any of the various alpha brushes available around the web. You can sculpt them in at whatever resolution you need for your final rendered image (though, honestly, when I need to go really high resolution, I move to ZBrush). You can then either bake these sculpted details into a normal map, or simply render right from the high-res sculpted model (generally speaking, your render times will be longer if you do that, though).