I am not sure what the phrase a fair speculation means exactly. Can anybody help me?

No, he wouldn't complain if they just dug a hole in the garden and shoveled his body in under the grass within reach of the rootlets. What 's your body? "They'll bury me all right when I'm safely dead. Try it; it's a fair speculation." "Try what?" The fruit merchant's countenance had suddenly set like a gargoyle in cast-iron. His half-brother had nodded toward a dingy portfolio that stood leaning against a half-empty book-case. And at that his guest had laid about him with a will. "So that's the kind of profit you are hoping to make out of your old bee-bush! That's your profit? That's your fine airs—your miserable scribblings and scragglings?" He had once more slammed down his huge fist on the table and delivered his ultimatum.

Walter de la Mare, The Tree, 192?

It seems to have been used in an older literature and what puzzles me is the fact I have found two different meanings to it in looking for the meaning; 1) a nice idea; 2) a good investment.

I think number 2. fits the context above but I am asking to be sure.

Thank you very much.