Here's a change to the GUI property picker I did a few weeks back.
It makes the values in the property pick 'live' (and also re-factors
the picker code to use less arrays, this should be obvious from the
diffs). A good demo is to open up the engine node and observe the rpm,
cylinder head temp, oil pressure and so on while playing with the
throttle and airspeed. It's pretty rough (some rounding of digits would
help) but useful for testing (at least I think so). I'm not sure about
the performance implications either, but it seems fine for me.