See in my eyes the testing of the performance of the design (that it does what is supposed to do) is simulation. To be able to simulate the entire confing with all the communication is what I expect from a simulator, because downloading the xcf to the control panel can be a real nuissance, but it is also time consuming. Plus you don't have any "debug" tools on the remote.
My xcf's are always hardware dependant, so without hardware my scripts do almost nothing. In this way I can't test scripts if I don't have access to the hardware with the simulator.
True you always have to do the final testing on the remote as performance on the remote is different than in the simulator.
Another benefit if the simulator works with the hardware is that you can develop your entire xcf before you order the TSU.
So I'm towards the idea of a fully functional simulator, otherwise for me is like developing a pc application that interacts with some hardware, without being able to use the hardware.