Many builders offer engine upgrades. Compare engine sizes between comparable size and type boats, or ask an owner or two if they're happy with the standard engine. Cruising catamarans, in particular, often benefit from extra horsepower. Investigate the pros and cons of a strut versus a saildrive, as well as the type of prop that works best for the boat. The boat's designer, builder, and dealer, as well as current boatowners, can shed enough wisdom to help you make the right decision.
Most modern boats have fiberglass engine beds.
Mechanical and electrical details. A dome light or two in the engine and drive-train area will prove helpful when servicing. Wiring, hoses, seacocks, and fuel shutoffs should be clearly labeled. If engine-driven refrigeration is included, check the service access and sturdiness of the system. Controls and gauges.