I've had four. Two 944 parts cars, and two 93 model 945 daily drivers - one NA, one turbo.
Trim and NVH levels are much improved over 740s. 94+ models got improved seals (plastic foam moulded seals) between the door frame and the door cards.
91 has a one-year-only fuel gauge and tank sender.
91-93 clusters will interchange, but note the fuel gauge is different on 91s. 94+ instrument clusters use different connectors to earlier models.
93+ models have a different auto shift lever handle, and different engine oil cooling and transmission oil cooling setups to earlier models.
93+ models have a round toothed timing belt and have L-blocks with squiters fitted. The method of testing the SRS system is also different from 91-92. The 93+ factory turbos also use a different intercooler to the 91-92 and 740Ts.
94+ steering wheel clock springs for the SRS are different to earlier models.
94+ also have a single in-tank fuel pump and some different wiring colour codes to earlier models.
94+ turbos didn't get a boost gauge nor ECC. The manual HVAC controller is vacuum / electrically driven, not cable operated like the 740 manual system.
Like the 700s, the fuel filler door design incorporates a stupid plastic hinge and is held to the body with even stupider plastic retainers. This is why many Seven and Nines lack fuel filler doors.
As others have said, heater fan motor replacement is much easier than on 240s. Beware of clogged drains. Note the 700 fan motor is different from 900s (2-pole connector on 900), and there's different heater fan versions for LHD and RHD. (Note the 940 LHD motor fits in RHD 960s, and vice versa, so there's plenty of stock of both from the usual suspects).
Heater core replacement is inevitable, and a total PITA to do. When ordering a heater core replacement from England (because they make the best ones and aren't ridiculous with their pricing) get the core with the long hooked pipes.
If you don't want to cook the engine, replace the standard 2-port heater tap with a 4-port Commodore heater tap,, so the water recirculates back to the head when "Recirc" is engaged. The heater core in 700/900 is designed to be a constant part of the cooling system, and cabin temp is regulated by flaps in the HVAC, not the amount of coolant flowing through the heater core. But some idiot engineer designed the heater tap to 'open circuit' the coolant flow path when "recirc" was engaged to promote rapid cabin cooling.... while ignoring the coolant needs of the engine on the very same days when coolant flow around the back of the engine will be most needed.
The cable tie is an inherent design feature of the 700 and 900 series.
