I owned a Niagara 35 and cruised on her in the Maritimes and to Bermuda from New York. I think it is a good design in this size range for offshore sailing. My opinions follow. I cannot tell you about how much repairs might be since I do almost all of my own work.
The more major ones are:
1 .Prop has stiff point and a wobble on the Volvo saildrive. May be a bent shaft in the saildrive, no idea if the bearings are affected.
2. There are symmetric areas on either side of the deck that are hollow. Either the core has disintegrated, or it was never installed. Perhaps the latter since it's a pretty even area with straight edges. Approx 8" by 36" on either side. Poor access from below due to the headliner. Looks like I'd have to cut open from the top if I wanted to fix it. Any chance I can just not fix it? The gelcoat is cracked in a couple places along the areas, but the fibres seem intact.
3. There are straps of unidirectional fibres that run down the hull to each keel bolt to help transfer the keel loads into the hull. (C&C had similar bundles) Many of them are not bonded properly to the hull in the bilge area and one actually has a large wrinkle in it. This appears to be a manufacturing defect. It seems to be virtually unfixable. without tearing out the floor and fully replacing the bundles. Seems like a huge job. I guess the question is whether this sufficiently weakens the boat that I shouldn't consider taking it offshore. Especially considering most boats don't even have these bundles.
More minor items:
4. There are three 2" diameter areas of delamination on the hull above the waterline. Probably manufacturing defects according to the surveyor (shear when removing from the mould). Looks like the core is probably still dry.
5. The Volvo 2003T is puking either oil or diesel on the water. Mechanic thinks it's probably the injectors. Any idea what servicing the injectors would cost?
1. and 5. A good question is how many hours are on the engine? I don't think that was the original saildrive so it comes down to hours and how well it has been maintained. Injector servicing is not expensive - a few hundred dollars at most. The drive problem could be quite expensive - call a Volvo dealer and see what they think the problem is and how much the parts would be. As was pointed out, Volvo parts are quite pricey.
2. Where are these areas of the deck? Since they are symmetric I would imagine that they are meant to be that way. Is it hollow (tap on deck to tell) or solid? Is it in a place where deck hardware might normally be installed (by the shape a small inner genoa track for example)? They may not have cored the area to allow for this.
3. I had these straps on a Nonsuch and Niagara 31 and 35 and in none of them was the attachment perfect in the bilge area. I suspect that this material is fairly stiff and while it would bend to follow a gently curved surface ie the hull did not follow the sharp bend at the keel. Could you post photos?
4. If the surveyor is comfortable with these spots then it should be ok. If the areas are easily accessible from the inside you could cut away the inner glass and add core material and then f/g over. If you got this done professionally it should not be too costly - as long as it is easily accessible.
A coupe of general comments. Do you have a purchasing broker? You probably should and he is paid by the seller (commission split). If not you might want to talk to Dave Harris In Oakville search for Harris-Ellis Yachts). He has been Mark Ellis partner since the 1970s and knows these boats intimately. He could tell you whether you are getting a good deal. I assume that you a purchase agreement subject to survey and sea trial. It is the norm when serious deficiencies are found that a new purchase amount be negotiated that reflects the work that needs to be done. Don't know how much flexibility there is (or what sort of deal you currently have) but the price should be lower with these problems.
I would also consider eastern boats. I did a quick check of Yachtworld and there were two Classics with asking prices in the mid 30s USD and one of these made a point of asking for offers. Some prices are higher. I noticed on in Fort Pierce, FL that is heavily equipped (eg genset and big chartplotter) but has a v-berth which may or may not what you want. I think that this boat might actually be onshore next to Ainia. If you decide against your current boat I could have a look at this one when I go to Fort Pierce in October.