The technique is to convert the image to Lab then use curves - drag in the white and black sliders one or two squares for bothe the a and b channels, then convert back to RGB. But it sure would be nice to have a script instead of doing all the steps manually.
This tutorial show how to do it manually.
Lab color boost

GIMP doesn't support LAB color mode, so there is no way modify LAB curves.

I have been working in a node based image processing application for windows that supports LAB color mode, and can apply curves and other adjustments to LAB images. This is a screenshot at imgur:

xXiELRZ.jpg

If you are a Windows user you can download the software from pixaflux com. I have also uploaded some videos to youtube. These are the hashes:

Introduction: ow8hd_vfUX8
User Interface: 9kLcUomESpY

Born2BeMild,
Get a boost in rgb color is totally possible. What would justify switching to LAB could be only one result, just got in that mode.

I followed the tutorial, converting to LAB and applied an overlay of 91.1 in the last step.
The result seemed like something I could get without having to switch to LAB.

If you use the same technique, and apply the same values ​​used in A and B, and contrast adjustments in L, for channels rgb and values, the result is very close.
Original left - Right using RGB

Below.
Using Lab - Original tutorial

Above are the results seen in Ho-Hum to Wow! in Gimp

There is the G'mic function

http://i.imgur.com/8xzu5X7.jpg

looks a bit daunting but if you stick with the marked sliders it is quick.

an alternative non-gimp is delabratory see parthas site for a link.

looks like this

http://i.imgur.com/eDnQzZn.jpg

big advantage is it is non-destructive so you can back off and re-do easily. If you do try, give the cmyk curves a go, IMHO better than anything else.

Thanks, yes I found I can easily do it in gmic but also downloaded delabratory to try it out.

If you want to separately adjust color and luminosity, you can split an RGB image to 2 layers, one color (AB) and one luminosity (L) and apply curve adjustment to it. You can see the result straight in Gimp.
ps
luminosity layer can be created by desaturate a duplicate with luminosity
color layer can be created by grain extract the luminosity layer and original layer, you then set this new color layer to grain merge on top of the luminosity layer (don't forget to set this layer back to normal before you playing around with curve)