1. Is the larger (and more powerful) dome going to be that much better (ie less clutter, etc) than the smaller one, for local coastal cruising.
Yes the larger dome with narrower beam width will perform better and return clearer targets. Will it make a difference when zoomed in to 2nm or less? Not much.
More concerned with spotting other boats and rocks / land than with weather fronts. In Nova Scotia, and we do have our share of Fog!
A 2KW will be fine a 4KW better, but not on the mast of a 30 footer!
2. Is the extra 16lbs of weight aloft (a little more than halfway up the mast) going to make a huge difference. small dome is 40 lbs, large is 56.
The boat is a 30' Seafarer, disp 8600lbs, balast 3450, large fin keel, draft 4'9".
I think you are quoting shipping weights. The 18" dome weighs 21 pounds and the 24" dome is 22 pounds. The big problem is the DIAMETER and getting your sails around it consistently and easily..
Note. Although I may not need digital or HD radar, I was pi$$ed to find out it is not compatible with my new (less than 1 year old) display. You need the new wide screen models, which were not available last year, to connect to them! I though I was buying a state of the art item. I realize technologies change, but i did not receive any huge discount, as if I had purchased aging technology!
Any advice would be appreciated!
Could have bought Garmin, saved money, and had a 36 mile, 4Kw, 18" HD dome and a plotter with an easy to use menu system..
Except for ST series instruments and my Autopilot I stopped buying Raymarine radars/plotters after my last bout with a C-80 system..