nords do have their own sound. i like it. i have a NL2X. great synth. pretty rich sounding and capable of lot's of bread and butter analog sounds and also it can get weird really easily.
i haven't played a JP in years so i can't recall what they sound like but i think they're quite different. if you are used to its sound and it has a place in your music you might miss it if you sell it. i think a nord is a good compliment to any synth for it's modulation ability and drum mode... plus, it's red
i don't think there's any reason to avoid the newer leads w/24bit dac. you might prefer it. the tone is the same but the newer ones are just a little more 'extended' if that makes sense.