Other Issues to Consider
Here are a few more things that will require horsepower:
Big Alternator - My E36RH has a Balmar 100 amp alternator that has a shut off switch because it can take up to 4 HP to drive it.
Bottom condition - always clean or growth accumulating all season?
Longer Trips - motoring all day to a destination or down the ICW to Florida. I'd rather cruise at hull speed at reduced rpm if I had to do it all day (or day after day).
Type of prop - If you like a folding prop like I do, a few more HP are advantageous. My E33RH displaced 9500 pounds on a waterline slightly longer than the 35-2. It had a 21 HP diesel that pushed it to hull speed at 2/3 max rpm.
Long Term Value - I agree with Christian. I consider the condition of the engine (low hours/repowered/diesel vs gas) one of the prime factors in determining the value of a used boat because the cost impact of repowering is such a large percentage of the total value of the boat. If you are planning on a restoration and using the boat yourself for some period of time, you will get to use all the benefits of the new engine and add value to your project for the eventual day when you sell.
Installation Cost/Effort - As costly and time consuming repowering can be, it just doesn't make sense to me to do it halfway. If I am going to commit the time and energy to the repower, I'm going to put in an engine that gets me the performance that meets my needs.
Put the 0.02 in your repower kitty!
Mark