Hi Rob,
If you are staying within one size of C-Dory (say, all 22's), then there is little difference in fuel usage between the various boats, as long as you stay with a 4-stroke or modern 2-stroke engine (E-Tec). So you can probably eliminate that as a comparison point.
The hulls are basically the same from 1987-present. Small changes to this and that were made along the way, but they are such that they don't change the overall character of the boat, and an individual might prefer various of them. What I mean is, there is no "known" better year or tweak. For example, I was open to any year boat from 1987 on up, but I did slightly favor those from around 1995-2005 (for my own personal, idiosyncratic blend of the various changes and features). But I would have bought another year range. My own personal highest priorities were stored indoors, the fewest possible accessories added, and no bottom paint; but another person could easily have different ones (again, no universal "truth" on which is best).
Our main size engines (typically either two 40s or two 50's, or a single 75-115) went from carbs to fuel injection in the mid-2000's (different brands at slightly different years), and that is considered a dividing point by many. I have a carbed engine and that's fine with me, although I would expect to pay less for a boat with a carbed main engine, all else being equal.
The Wallas combined stove/heater seems to be a love it or hate it sort of thing. On the one hand, it does both, and takes up precious little space doing so. You can easily take along extra fuel if you are going on an long trip (say, Inside Passage). On the other hand, they are the opposite of "a flame and a tube" (basic stove) as they have a lot of parts and circuits, etc. They are expensive to buy (so good to have one on the boat already if you want one), and a bit more expensive to maintain (vs. a flame and a tube). They take a while to heat up for cooking (say you just want to boil a cup of water on a hot day), and just in general, a combo thing never does the job as well as two separate things that are each dedicated to one job.
So, some folks LOVE them (and for good reasons).
Some really don't like them.
I'm somewhere in the middle: My boat came with a Wallas and I just knew it would drive me nuts to wonder if it was going to work or not, plus I often just cook something quick (not the Wallas forte). So without even giving it a chance :wink , I removed mine (and sold it to another C-Brat who falls into the first category). I carry two devices (one for cooking; one for heating).
Newer boats are worth more. A lot of that is because they are... newer. As you would expect. But unlike buying a 20 year old car, you actually can buy a 20-year-old C-Dory 22, and if it's in great shape, you aren't buying something that is going to seem as outdated as a 20-year-old car, because they haven't changed that much. Also, as long as it is in the budget, it is easy to re-power, change electronics, etc. (whereas you really don't do that on a car). So really, any 22 could be a good one, just depending on condition, rigging, and what you personally want.