So, I'm wondering... For coastal sailing in LIS and very occasional forays to
open ocean points north of there, do I need anything more than Furuno's model
1623?

Joey

Need: If you're sailing in areas where you are doing night time or occasional
sailing in fog, you could make points for and against radar.
Certainly, radar can make things easier.

Afford: You need to look at many things here, not the least of which, is your
wallet, but you also need to know what you can afford to put on your boat,
considering space for components and power requirements, coupled with your own
comfort level of viewing and using the unit .... you may end up being able to
go high end, or have to settle for low end .... only you can say.
Once you decide on a set (if you're thinking about it, you'll probably end up
getting it), keep in mind that the installation, to suit your needs or
financial requirements, is only the beginning ..... now you need to learn how
to use it.
My quess? 90% of those with small boat radar, get a maximum of 50% of the
capabilities/ advantages, that a radar can give.
Between not knowing how to tune for conditions, not being able to interpret the
display, not understanding relative motion and plotting, and thinking that
since they have radar, they are now safe, a high percentage of those with
radar, are more dangerous, now, than when they didn't have radar.
It's a great tool, but you need to understand it and know how to use it .... if
you don't, it's a waste of money.

Shen