I'm assuming that whether we are talking panoramas or more usual photographs the issue at question here is not related to that, but rather to the relative effects of making luminosity tweals in RGB Luminosity versus LAB Luminosity - right?
Exactly. The point is, that color integrity is not maintained (can not be maintained) in RGB. This means, that if you change the luminosity, the color changes as well,
except if all non-zero components have the same value. Grey, red, green, blue, yellow, cyan and magenta remain grey, red, etc.
There is no such problem in Lab. The other side of this is, that when converted back to RGB, the change of luminosity becomes non-linear. I don't find that a problem, particularly because any contrast enhancement changes the luminance proportions anyway, so the integrity of luminosity is a moot issue. Although this change does effect the contrast to some degree, I have never seen this as an issue, but I can imagine applications, where this might pose a problem. However, color integrity is IMO more often an issue.