Same answer here really,
Buy a synth for its personality, every synth sounds different, I hate songs sprawled with the same synth sounds.
On a financial note, i guess get more for your money though bear in mind quality, the jp is a quality product though lacks in polyphony and multitimbrality, though I knew what i was buying before i bought it, I knew how lovely and warm the bass sounded, i was blown away with the feedback oscillator screaming arabic style feedbacks at me.
I havent had the chance to check out the yammy , though if it feels right at the time buy it, I think synths , like anything, are a personal preference.
peace
dafluxtah