Thom / Don
You are right, I forgot to mention the SC20. I sailed a friend's SC20 a couple of times and the boat is as good as you say - and used ones can be found relatively cheap.
If it can be kept with the mast up by the beach, the SC20 is a great choice. If you need to trailer, though, its width makes it more complicated then the ARC21.
By the way, the SC20 owner, now over 60, says that he does not like to mix daggerboards and sand, so his next boat will probably be boardless, like a SC17 or that 18 ft rotomolded boardless French Hobie (I forgot the name).
His current definition of a good boat is a boat that is as basic as can be - and he is probably right. This guy sold his HC21SE (definitely not a good boat for offshore sailing) when he capsized five years ago, hit the wing and broke some ribs. That beast just can't be righted without help... he bought a used SC20 and now I am trying to convince him to move into a folding tri - which is obviously a safer and more comfortable boat for offshore sailing, especially if you want to sail until you are 100...
If the person who asked the original question is still reading, maybe a bigger boat is a good choice, if you can afford it. In this case a folding tri is definitely the best choice.
Cheers,