I really would like to learn how to play reggae, but I find the more reggae songs I learn the more I realize that they are just bar chords.

But they really don't sound the same when I play them.

What are some good techniques for writing/playing reggae?

I think its tyhe same principle as Ska. Muted downstrokes to get that rythymic "click" and play the upstrokes. Barre chords ofcourse
Personally I think you should play it however you feel like playing it bro. It's good to know how the other bands play it, but when it comes down to it, you want it to be something of your own.
I play in a band and we do a lot of reggae and ska stuff and I have even written a couple songs.
What I do is listen to a bunch of reggae, ska, rock-steady, etc. to get in the state of mind and get a little inspiration.
Then i get away from it all and try to come up with something.
Hope that helps at least some bro.
Try playing on the 2 and 4 beat and try barreing you finger over the bottom three strings for your riffs ( gives it a very Ska feel which i`ve heard is very similar to Reggae ).
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Try playing on the 2 and 4 beat...

a very good point
i'm not one, but if you're a counter: mute or don't play the first beat and the third beat
that way you are playing off-beat (second and fourth)
so: 1=mute, 2=play, 3=mute, 4=play