What I feel you have to weigh.
- lower operating costs for fuel, oil, plugs
- Easier (usually) to access to do routine and not so routine maint.
- can be harder to dock depending on wind and current
- extra engine to get you home
- easier around the dock.
- more weight to trailer
- two of everything to service, including drives
I went with a singe because at the lake I wasn't too worried about having to limp home. Just tow me to the nearest marina if I break down. It would be different on say the ocean or the great lakes. Also with my boat a single 575 will outperfom twin 496's in the the same boat (not HO's) with less fuel burned. maint will be a bit less with my single because you have to add in the SC. Also my boat weighs about 1000 lbs less with the one engine and there is easy access to everything that requires routine maintenence.
Finally it will depend on the size of your boat the bigger the boat the more rational twins become. What are you and Lutz looking at?