OK, here is our story.
Last year (for the second time in 9 seasons) we must have had a "near by lightning event" of some kind. In the spring during commissioning I noticed that a bunch of the electronics that had worked perfectly the previous season had failed. My MacIntosh radio and amp, the espar control unit and a Balmar voltage regulator had all gone to their reward. A month or so later the E-120 began acting up and the pilot failed (control unit). As we were about two weeks from heading out for a month we elected to replace the Raymarine components. Of course the new plotters will not work with the older units so in the end we purchased two plotters, a radome and the autopilot! Can you say ouch!!!
So to answer your question, yes there is a discernable difference in the 2 Kw radar and the new RD418HD (you are correct, it is a 4Kw, I forgot!). To tell you the truth I was expecting a more dramatic difference than there is but I have noticed that target definition is enhanced (small converging targets) and the color is very nice as it too adds definition to the display. The other thing I noticed was that the automatic gain, sea clutter and FTC controls are cleaner and work better. The plotters are much faster and in general, it was a nice if expensive upgrade.
I am very happy to report that the MacIntosh gear was salvaged (it only took two trips to the repair facility in CA!) as it is no longer available…
Bruce