Crack in the stern deck is probably just cosmetic and is repairable - we are currently repairing several deck cracks on our 170 right now (will post some photos when I get a chance). The one near the bow would be a bit more concerning for me, wondering if the structural integrity is compromised. That area takes some stress from the nearby standing rigging attachment and the mast step.
I would want to look at the inside fiberglass lining in that area - if it is solid then you can just repair the surface plastic and be fine. If the fiberglass is cracked I would have some concern.
One way to get a look inside is to remove the forward cup holder and reach into the cavity below with a small hand-held camera (or even a phone with a flash) and take some pictures looking back up into that area. Here is a video I made doing this on our H170 recently so that I could assess the condition of the interior as we were making other repairs:
http://youtu.be/7FegO5UjVlI
Later we actually went a step farther and created a small "sled" for my iPhone with strings attached and ran it from the forward cup holder all the way to the stern to get a good look at the entire inside. Made me a bit nervous about losing my phone, but it worked great.
