Yes you could simplify quite a bit.

If you don't need any special effects, it is sufficient to plug the image into Ambient_Color (set the color chip to white) and adjust brightness with Ambient_Value. No other nodes are needed.

I like the HSV node in front, though, because I sometimes adjust saturation. (Usually to get more or less blue in a sky)

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)