If you can afford the Jem Platinum, go for it. I was at a quilt festival last June and they were having a special on them, $439 plus they were throwing in the walking foot and some other feet, so it was a really good deal. We called two ladies from our quilt group and ended up bringing 2 Jem Platinums home with us for them!
Janome is having new machines come out on May 1st, so maybe the Platinums will come down even more after the new machines are launched. Actually, you might like one of the new machines that's coming out, because it's a lightweight model.
Oh yes, and like the other ladies, I absolutely love my Jem! :D