I agree that it would be useful to have as many properties as possible available at runtime.
Unfortunately (for one of my projects), I've just discovered that some of the existing properties available to change at runtime don't appear to work.
For instance, if you have a bunch of sprites at the top of the screen with the Physics>Gravity disabled, and then try to enable it through a keypress event, nothing happens.
Similarly, if you have a bunch of sprites at the top of the screen with Physics>Immovable set to true, shooting missiles at them means they don't move (which is correct), but if I change the Immovable property to false via a keypress, there is no change when missiles hit them (i.e. they don't move when colliding with the missile).
Either I'm doing something wrong, or hardly anyone bothers to use the physics aspect of Construct, and that's why it's gone unnoticed.