My cat's currently being treated for lymphoma - I agree with you about quality over quantity, but in her case the reccomended protocol is fortnightly chemo in tablet form and daily steroids (and steroids are how I was told they'd treat palliatively anyway) I don't know whether the chemo's done anything yet as she's not due her 2nd dose till Wednesday, but it hasn't given her any side effects whatsoever.
I know you've said you're not treating, so that's just me waffling, lol.
So, the steroids are definitely making her feel better, we noticed she was I'll because she'd lost a bit if weight, her coat was looking a bit dull and she wasn't as playful, in the fortnight she's been on steroids, she's put weight back on, her coat looks much better and she's much more active - which I figure is good, lol, and they should make your dog feel better for a while too I'd have thought.
I've read that a high protein diet is good, so food might be worth looking at... It might make not a jot of difference giving her food with a higher meat content, but I figure it won't hurt and it makes her happy to be getting it ( yep I'm spoiling her because she's ill, lol)
I don't know if that helped at all, but I had my dog pts 6 months ago because he had cancer in the soft tissue of his leg and because of his age and arthritis in his back hips, there was no treatment that wouldn't have affected his quality of life - so I just wanted to answer, it was horrible :( it was a case of pain management until it was the right time and I'm happy it was the right time, but I still miss him.
They don't half worm their way into your heart