I've been thinking more about what I think these stimulants actually contribute to my health in recent days, since starting this thread.
I think it's more a case of them helping me to continue for longer at whatever reasonable task I set myself. Of course the nicotine doesn't help with my appetite - I realise that it deadens appetite when I really need to 'stimulate' appetite; but I do feel that combined the caffeine and nicotine (both of which I enjoy or rather I love coffee and am pleased now to be able to tolerate it once again) help me fight against the fatigue.
Like you and others have implied/said however; they don't negate the primary cognitive symptoms. I still have issues with reading for example; but I can on occasion read for longer. If that makes sense. Neither source of stimulant means I can avoid my rest periods and neither do they eliminate the exhaustion completely.
I also reach a point where I simply can't continue. It's just that that time is delayed a little longer. Plus of course I gain from the pleasure of drinking and enjoying my java