Camera sensors can usually capture rich saturated colors and fine detail if you give them a chance.  The issue is the amount of time the sensor has to record that information.  Long exposures can sometimes help you capture a moment that otherwise would be lost.  Here are some essential steps that help make this type of photography fun and satisfying:

Sturdy Tripod - there's nothing better than a sturdy tripod to mount your camera for any exposure longer than 1/60th of a second (some would argue 1/125 is the minimum shutter speed, but with vibration and movement reduction lenses, it becomes less of an issue).  I've tried holding the camera on a fence post or against a car door or tree, but inevitably, even the slightest movement will ruin your sharpness.  Best to get a decent tripod and let it do your work.

Low ISO Settings - most modern cameras handle this very well in that a high ISO setting on your camera (beyond 1600) doesn't reveal too much noise in the photo, but the lower the ISO the better for long exposures.  This is especially true for exposures longer than 30 seconds.  There is a balance that must be reached between ISO and exposure time.  In the photo below, an ISO setting of 100 was used for 30 seconds.  This really helped in the post processing as the noise clean-up was minimal.

Exposure Time - this is very difficult to estimate, and requires trial and error, but luckily there are some tools to help.  Many modern cameras have an exposure meter that will actually tell you if your photo will be under or over exposed based on your current settings.  Set your camera to shutter priority and dial in 5 or 10 seconds to begin with.  Take a look at the exposure meter in the viewfinder to see how far off you might be.  Review the photo and look at the histogram if you can, and adjust the shutter in 3-5 second increments.  The end result should be a photo that is still a little dark, but that's what you want, since over exposing will wipe out much of the color and detail you're striving for.

During post-processing, you may need to lighten the photo a bit or increase the exposure to make it brighter, but ultimately, the dark rich beauty of saturated colors from a long exposure will prevail once you get the hang of it.  

Dusk on Smyth RoadThe stillness and soft glow of a summer sunset near Mount Vernon really rejuvinates your spirit.