To answer your exact question, is it worth it to spend money to get better than +/- 24 feet accuracy? The answer is no.
Really, even +/- 50' is more accuracy than anyone needs. Most charts are not that accurate, so knowing where you are on a chart that is not that accurate doesn't really help you. Do you really think that a rock or jetty or nav aid listed on a chart is accurate to within 25'? They aren't.
Personally, I try to stay at least 100' away from ANY hazards, and usually I can stay much further away from them than that.
Originally Posted by mm2187
How accurate is your GPS. I have a new Raymarine A67 chart plotter which I love. When mounted on deck without an external gps sensor has an accuracy of about 4-10 feet. When mounted below deck it has an accuracy between 8-24 feet without an external gps. I plan to mount it below deck without a external gps sensor. With an accuracy of +/- 24 feet on a 40 foot is it worth the additional money to get another few feet of accuracy?