What to look for when buying one used. The one I'm looking at has 65k original miles and a 6cyl and hasn't been molested.
In the 80's CJs, AMC hadn't quite perfected computerized controls for everything. So, most things were controlled by plastic vacuum lines. These vacuum lines became brittle with heat and time, so by now most of them will disintegrate if you look at them funny. Plan on spending a LOT of time tracking down vacuum leaks and replacing with rubber vacuum line. This was especially true of the GM 151ci 4 pot that AMC used (the only 258 I had was a Clifford fuelie conversion, but I would imagine it would be similar).
That was really my only complaint about the CJs. There was a lot to like about them, especially if it's going to be primarily a pleasure cruiser as you suggest. I liked the raw simplicity of them, I loved the interior, and I loved
the top-off experience... yes, somehow it's better than a TJ or a JK. Can't really pin that one down. For reference, I have had all 4, '86 CJ-7, '84 CJ-7, '92 YJ Sahara, '03 TJ X and the current '07 JK Sahara.
If you are looking for a simple CJ purchase that you don't have to put much thought into, look for one that is as close to stock as possible. Know that you will have to do some basic maintenance and will be tracking down vacuum leaks but otherwise stick with the 258 and you'll be fine for your stated purpose. Just don't plan on morphing it into anything other than boulevard cruiser/dusty trail goer, otherwise you will have a "project" on your hands. Also, remember that '86 was the last year for the AMC CJ, and the company was in it's death throes, so maybe not the best year from a build quality standpoint.
If you are looking for a "project", I really like the 2k2's idea of a YJ front clip conversion. Or, build up an early TJ (probably best basis for an off-roader).
But that's just like, my opinion, man.