I have created a plugin that applies an autolevels effect to the krpano view:
http://fieldofview.com/projects/krpano_autolevels
The effect can be tuned to affect just the luminosity of the view, or the luminosity as well as the color of the view. Please note that the effect is applied to the (jpeg compressed) 8 bit panorama, so if the effect is too pronounced you will start to see artifacts such as banding and color mismatches. There is a number of parameters that will let you tone down the effect to suite your images.
The autolevels effect achieves a similar effect to the Adaptive Dynamic Range concept (ADR) which I previously implemented in SPi-V, but instead of mixing dual exposures, it applies a color transform to the view after it has been drawn by krpano (but just before it is displayed on the screen). This has the advantage of being simpler to author, but has less control and less actual dynamic range than a full ADR implementation.
The plugin requires Flash player 10 or newer. It can be used free of charge and its source code is available under a CC-GNU GPL license.
The autolevels.swf file and its sources are available as part of the krpano_fovplugins package on github.