A remap is worth it in that the car will be better to drive with a nicer torque curve. You will also get 10-14bhp, which doesn't sound like a lot, but it will be a more satisfying drive which is the main thing. Note that the 2.2 JTS is hard to remap as it can't be done via the OBD port, so not everyone can do it. Red Dot can, AUtodelta could (not sure if they are still trading?) and I think Angel could, but I don;t think Angel were doing custom maps. A custom map is where they test the car on a rolling road and make changes to the map, test again and re-tweak the map. Red Dot did this for me and I liked the map a lot.
You can do various exhaust mods, depending on what you want to acheive. If you just want to improve the sound, you could get Brera S back boxes. If you want to improve performance, you could remove the centre silencer altogether, or you could get an entire catback stainless steel straight-through system, which will make the car louder, but a good fitters should put proper silencing in to make sure there's no drone.
Whatever you do, get your exhaust mods done before you get the remap. THe remap can then be tailored to get the most from the car's new exhaust set up.
You might also consider changing induction. I found that the 2.2 ran a lot better with a 76mm internal diameter K&N cone filter (available online from Demon Tweeks) instead of the big old factory air box. It sounded fantastic and ran smoother. Or you could keep the factory air box and put in an aftermarket panel filter. You will only get a verym small increase in performance and sound that way though.
Again, do induction changes before remap. Do all 3 changes and the car will improve quite a bit. but it really depends what you want. If you just want improved sound maybe get S back boxes and consider changing the induction.
Worth it in a Spider even more than a Brera
Some more questions from me:
1. I presume a remap isn't worth it? I've had several of my recent cars remapped with good results (including ones with N/A engines). Sometimes the remap was done purely for performance (turbo boost pressure) and at other times the remap was done to make the car more enjoyable to drive (mapped to a specific fuel, linear throttle response, etc).
2. I haven't even heard the exhaust note of the 2.2 JTS Spider. Are there aftermarket exhausts (cat-back) that improve the sound? I'd be looking for a sporty, rasping sound rather than a deep rumble.