Renovo is good for removing the sort of fine scratches which one gets when some silly ****** has been using paper tissues to clean the windows.
Incidentally, the usual window material is polycarbonate, I think, rather than perspex. Perspex is flimsy stuff.
Never tried it with milky windows. However I have read, in a different context (restoring certain clear plastic car headlamp mouldings which go milky through water absorption and cost £hundreds to replace) that the milkyness can be removed with exhastive (exhausting?) power buffing.