Mike --
I did not, and do not, disagree with anything you or the others above have written. But I did add two things to what you said -- I directed him to resources he might draw upon (as he asked for) and I pointed out that sponsons and 18' length might be assets for his intended.
I merely pointed out that someone interested in sailing a canoe might prefer sponsons and an 18' long boat. Indeed, such a hypothetical person might not be interested at all in a boat without sponsons, and indeed, such a hypothetical person might not pay anything for a smaller, more easily- swamped canoe.
Canoes are not sold by the yard -- they are built for, and sold for, specific purposes, and usually a canoe designed to meet a specific purpose will be worth more to a buyer than one that doesn't.
Why would anyone wanting a 16' canoe without sponsons even look at this canoe -- it has NO value to such a person except possible resale value -- and the OP does not seem to be interested in buying a canoe for resale.
But a person looking for a sailing canoe might actually pay a premium for a sponson over an otherwise similar canoe, given that sponson canoes are not all that common. As to weight, well some people regularly buy much heavier boats, including heavier canoes -- "war" canoes and Grand Lakers, for example, and pay the going price for such awkwardly heavy boats, and devise ways to deal with the weight, which is part of the package they buy. (They don't usually car-top such canoes -- some exceptions, of course -- but use a trailer or truck.)
As the link you give makes clear, there are many variables going into the price of a canoe. Sponsons are not generally desired, are often removed, and can detract from the price of a canoe. But generally, someone who does not want a sponson canoe simply buys one without sponsons -- there are a lot around. And not so generally, some folks actually want a sponson boat, and go looking for one. The exception (of course there are always exceptions) is someone who primarily is looking for a boat to restore and may not pay much attention to unwanted sponsons, because they are fairly easy to remove during the course of restoration.
I agree that this canoe is not worth $900 (or even $650, taking into account the putative value of the paddles). The chief negative factor most of us would consider is the fiberglass covering, which most of us would want removed -- usually a messy, hard job. And for most, that is an overriding consideration, no matter the intended use. And further, without a fiberglass covering, I, like you, would expect to be replacing those repaired ribs so near the turn of the bilge -- they are probably done with a very short scarf, if any, and would need to be replaced.
If I were interested in a sailing canoe, and if I were considering canoes that needed restoration, and if I were to consider this one at all (not likely), it would only be for a substantially lower price, and (another variable) I would not pay much attention to the value of the paddles much at all, having more paddles than I need already (well in excess of 20).