There are plenty of things that you get by spending more on a camera body. It is up to you to decide which one is important to you:

• Sensor: The sensor is the most expensive feature. Bigger sensors cost a lot more and give higher image quality. Depending on the model, you may get superior low-light performance, higher-resolution, higher-dynamic range or a combination of these. New higher-resolution sensors cost more than those of the same size as well.
• Viewfinder: The second most expensive feature on a DSLR is a 100% viewfinder. This lets you see the entire scene before shooting while most cameras show 95% of the scene. This means that unwanted elements may appear in your images after shooting. Count on $300 to $500 extra for this feature alone.
• Weather-sealing: The third most expensive high-end feature is weather-sealing. This lets you take the camera in the rain, snow and sandstorms provided that you purchase weather-sealed lenses as well. This can become extremely expensive as the cost accumulates per lens.
• Dual control-dials: Mid to high-end cameras have 2 control-dials as opposed to 1. This makes it more efficient to control and adjust exposure.
• More buttons: More external buttons means relying on the menu system less. Each time you enter the menu system it slows you down. Advanced cameras are designed to be used efficiently and under pressure and therefore have more buttons to keep more functions at your fingertips.
• Build: Advanced cameras are expected to be used and abused more. They are built tougher to last longer. You won't see rotating LCD displays on true high-end cameras because it is a serious point of weakness. You will see cameras built with magnesium alloy frames, rubber-coated on more sides and with more wear resistant shutters (between 2 and 6X more shutter-actuations).
• Continuous Drive: Higher-end camera usually shoot continuously faster and always shoot much longer bursts (over 100 frames for some) compared to lower-end cameras.

There are plenty of minor differences that depend on firmware as well. In other words, differences that manufacturers introduce to differentiate their products while the hardware is capable of more. These include the number of stops for exposure-compensation, number of images in a bracket, metering modes, customization options, white-balance fine-tuning, etc.

I am certain I forgot some but these are all the most important differences.