While I will agree that the outboard does take away from the looks of the boat, it's not that bad. It's also not that difficult to control the outboard from the cockpit. My old Honda is much quieter than the Renault and is very smooth and extremely reliable. The Renault will rattle your fillings at lower speeds

Rebuilding the Renault is a difficult task at best. It's close to 30 years old and it has been somewhere around 20+ years since manufacturing ended. Granted some parts are generic and can be sourced with research (seals, possibly some bearings, etc). Other parts would have to machined. The transmission cones are no longer available apparently.
One of the biggest problems is that the cost of a diesel re-power can easily exceed the value of the boat. Take for instance my case, if I have a new Nanni, Beta, Yanmar, or Westerbeke installed, it will cost painfully more than what we paid for the boat, even if I did the install 100% by myself. I sometime see 27's for sale that have a good diesel that could actually be purchased for less than the price of a re-power. So what's more cost effective, buying a new engine for the price of a whole boat, or buying another boat with a good engine then selling, donating, or scrapping the one with the old engine?
That being said, when I can, I will re-power mine. I plan on keeping the boat for a very long time and I would rather have a nice inboard than the outboard. I keep hoping that alternative means of propulsion will become more viable and affordable (electric power maybe???) but I always look at the Annapolis boat show at the small engines and I keep thinking the Beta is the way to go for the 27.