GPS Anchor Alarms
I think that the extra accuracy claimed by the newer units is not that significant to boaters. If selective availability (induced position inaccuracy) was still in effect, a WAAS or differential GPS would have tremendous advantages. Now, I suspect it''s mostly marketing. They didn''t know that SA was going to be turned off when they developed these things.
That said, get a new GPS, one with a charplotting capability. Almost all new GPSs have some sort of charting built in. Having your position imposed on a chart, no matter how small, is a powerful thing.
Also, the expense of any GPS is dwarfed by your investment in learning to use it, and the time you spend entering your own routes and waypoints. That means that whatever you buy, you''ll someday be reluctant -- like me -- to give it up.
So, get the latest and greatest, but not necessarily the most expensive. Learn to use it really well.