I want to repower but...

[Handful in NC]

On the Etec big single bandwagon... after 2 1/2 years with my Tsunami/Etec 250, the ONLY maintenance has been to adjust a stretched shift cable, which would not be an issue with the fly-by-wire version. It always starts immediately, and never sputters, smokes, or misses. With two people, light gear, and half fuel, I get about 30 mph at 10 gph at 4000 rpm. Tops out in the upper 40s. I have seen over 50 mph. With 8 people and beach gear (chairs, bags, and coolers of food/beverage) on board, there is plenty of power remaining without pushing the engine. It lives in salt water and is run regularly year round. Simply the best boat motor I've ever owned, and perfect on my Tsunami.

[Billpotter]

In my opinion, the 23 hulls seem to be happiest with a big single. She was designed when outboard twins weighed 600-700 lbs. combined, and were required if you wanted outboard power on the 23 at the time. Modern big outboards seem to weigh about what the twins of forty years ago did. The only reason I went with a twin set up on my current 23 project is that we spend significant time in the Bahamas where there is no Sea Tow or Boat US, and I wanted to be best prepaired for the possibility of an engine running/ gear case/ prop hub problem, and wanted to be able to get back to port without relying on good Samaritans or the Bahamas Air Sea Rescue Association (BASRA).
To adjust for the combined 860 +/- lbs of combined engine weight, I raised the weather deck 2.5" and installed valves in the reconfigured deck drain system, split the gas supply into a forward 50 gallon gas tank ahead of an under console step down, with a 70 gallon gas tank aft of the step down in large part to be able to keep weight out of the rear of the boat to compensate for the additional engine weight when I wanted to. I also redesigned the stern area, and had a complete stern module/ assembly mold/ part built and installed that provides for a motor well front that is 2" above the level of the 30" transom with a water tight motor well door to keep the water out: The additional 200 lb. +/- of engine weight makes a big difference.
If a nice 23 is for sale, and it has twin engines , and is a nice boat; a nice boat is a nice boat: for general use, I'd buy her.
If I was setting up a boat for what I call "car boat" use- a boat folks will use for everything; family, cruising, fishing, hopping over to Bimini, etc. (within the stated range of the two tow services), I'd readily go with the single. If I was going waaaaaaay offshore, I'd consider a well thought out twin set up.

The boat will be happier, the maintenance costs will be lower, and the fuel economy will be better with a modern efficient single outboard.