I've seen that ad; I almost convinced my wife to take the short ride over to look at her!
Take a look at this example:
1968 Pearson Renegade sailboat for sale in Colorado
Seems to me that this is a classic case of someone putting an awful lot of time and money into a boat, and wanting to get some of that back. Regardless, check out that door to the head!
Wow! Ads like that make me sad. You are 100% right that the guy obviously put a whole lot of money and work into this boat. And while its easy to argue that way too much was spent on things that do little or nothing good for the boat, the sad part is that this is an outboard motor version, which combined with the length and age of the boat limits is price to about a third of what he is asking for the boat. I hate seeing things like this. It gets to the heart of my point earlier about the fact that most decent boats can be fixed up to be really nice boats, but if you are the one doing the fixing, its next to impossible to recover anything resembling the money and time put in.
But beyond that, as Jim rightly says above, the virtue of these boats are that they are simple, and that simplicity is what makes them reliable, inexpensive, and easy to work on. If you feel that you must restore one, and if you can try not to get too far carried away, staying close to the original concept, and not try to make a new boat out her, and can live with the understanding that part of the charm of an older boat is that she is an older boat and doesn't need to guilded and garnished; when you are done you will still have a nice boat to sail and own. If you can spread out the work over time, the old girl will only get better as you own her and will owe you nothing when you sell her for a fair price.
But boats like this, over done in some ways and under done in others, are impossible cases because in the end only an idiot with money to burn would pay anything near $30K for a boat this old, this size and this limited. Which is a real shame, since I can only figure that might be what the seller has invested in the ole girl.