Welcome to the club! You are not making a mistake buying an 86 vs an 87. They are basically the same car with a different front grill being the most notable difference. Although much fewer GN's were made in 86 compared to 87, the current market value between the two are the same. As time goes on one could make the argument that an 86 has the potential to become more valuable based on production numbers (5,512 compared to 20,193 for GN's), but so far that has not proven to be the case.
Google says 35k CDN is ~27k USD. Before purchasing any GN in that price range I would first look at what you intend to do with the car. Years ago I was in a similar situation, what to buy as my first GN... At the time I was set on buying a low mile, completely stock GN. I ended up buying a very nice, low mile, almost completely stock car with exception of an aftermarket intake and exhaust. As much as I loved my new purchase, I was always somewhat disappointed with the performance of a stock GN. After 4 years of trying to keep it "pure" by only buying factory replacement parts as things started to wear out, I realized how trying to stay as close to factory stock, in the purest sense, was near impossible. It was at that point I said fuk it and started to mod it a little. I limited the mods to only a few bolt-on's but I will tell you that I enjoy driving my car much more now than when I first bought it!!
Moral of the story is, if you're planning on buying a GN just to park it and stare at it, you can find a near mint condition car for 27k. If you want to drive it and enjoy it, you can find a good one for a lot less. If I could do it all over again I would buy a car already modded to my liking or close to it. There are certain reliability mods that should be done to every GN (fuel pump, chip, timing set, etc.). The problem all new owners face is knowing whats good and whats not. That's where experience and this board come into play. In time you will see that these cars are unique in terms of what makes them tick and we have access to some of the best Turbo Buick experts on this board to help you with that. Answers to most questions can be found using the search feature. If you can't find the answer you're looking for, just post up. Anyway, sorry for the novel. Enjoy hunting for your first GN.