I definitely think the upgrades merit twice the price. It will be several man hours to overhaul those systems, and it will still cost a pretty penny.
If the boat is in really bad shape, I wouldn't pay more than a few thousand for it. Mine is in good shape, but I'm finding that I'm still pouring quite a bit of money into it.
As far as I am aware all CL teak decks need to be removed and glassed by this point. I'm sure they look sweet in pictures, but if you get up close, you're probably going to find them irreparable. And you really don't want all that water leaking into your cabin through hundreds of tiny holes.
The Volvo seems to be holding up well in my case. I don't know much about their overall reputation. Mine only has 1,500 hours on it but I've heard most diesels can go well past 5,000-8,000 hours if taken care of. They are still serviceable and it's easy to get parts.
Cabin headroom is great. Through most of the cabin I have 6' 3" of headroom. Pretty good for a 30' boat.
Let me know if you have any other questions.