Craig,
A radome is basically just a small open array inside a dome “cover”. It has to shoot through the dome, which is not as good as an open array version that does not. The dome works well for small boats, as the moving parts are inside and less likely to get damaged.
I have a Furuno 4 kw radome, and from what I’ve seen on friends boats it is much better then a 2 kw unit. I know an open array is still better yet, but I didn’t think it was necessary for me. And I still don’t. I am very happy with my radar. I can see every little buoy and mooring although if you remember I did mount my radar up higher then most on our size boats. Unless you need to see birds, which is a whole different ballgame in my opinion, I would think a 4 kw radome would be just fine.
By the way it was great seeing you and your wife at the island Saturday. Hope you found some fish. We got a few dodo's out around the Avalon bank.