Not a bad effort at all there Dave. The 40d does hit it quite hard especially with cooling, you should try and nock up the ISO to the next level if you have cooling! that way you can take nice short subs, with the cooling subduing the thermal noise.
The only other thing i could say about the processing i dunno if you touched up the dark neb or not, but it looks overly black considering the sky around the weed, if you have given it a little pep, you might want to try this method in PS.
make a duplicate of the layer and sit it above the back ground,
change the layer mode to soft light
put a layer mask Hide all
with the paint brush on white (25% opacity and 25% flow), and the layer mask selected, start brushing the areas to be darkend/contrasted.
Be light handed with this method as too much will bake the image, also keep flicking the layer visibility on and off to see what you have done and how far you have pushed it. I find it always makes those nice little dust lanes pop out without looking stupid
Good luck and hopefully your wife will congratulate you once you pop out a award winning image!