thing is where the JTS is concerned in terms of being a tunable engine, its basically not without spending a huge amount of money, the remap will deliver a bit and if your JTS is chucking out the claimed 165 ponies then 177 bhp is a respectable figure and it will be an enjoyable drive without ever really setting the world alight, the biggest gain will be crisper sharper throttle response.
if I were you I would concentrate on getting the best out of the handling as although the JTS is the same block and head as the diesel it benefits from not having the weight of the turbo related stuff stuck to it, believe me I have had the turbo and manifold off my car and it weighs a good 30-40kg, add all the diesel emissions related stuff ,plus the weight of the intercooler and oil cooler which your car does not have it will be a good 65-70kg lighter, crucially over the front wheels where the handling is most affected.
my old JTS GT felt lighter in the nose than my derv and a bit more ''direct'' but in terms of unlockable power the derv is on another planet.
so if you are going with the re-map, I have a couple of suggestions if you are really serious about getting the best out of the car.
1) have a look at more direct induction route and replace the air filter with a K&N performance one.
2) a sports exhaust will get the air out quicker which should make the most of the re-map, consider a pre cat delete..as well £300-600
3) eibach Arb's to cure the body roll on stock suspension. £300
3) lowering springs either with stock shocks if money is an issue ,or a set of bilstein or similar. £200 if you stay with stock shocks
4) if the clutch is due maybe take advantage and have a lightened flywheel fitted or have the one on it lightened...not sure on this for the JTS but £300 feels about right
5) short shift kit will improve your progress as you will get through the gears cleanly and slickly...again not sure on the JTS gearbox, if its the C630 gearbox then there is now a stainless steel one available for £40, (check out the GTV section) easy to fit and a good mod to do in conjunction with the re-map.
6) the only other way to make more power ''affordably'' would be some fast road camshafts. budget around £600 all of that should see you with a peak figure of 190-200 bhp. which would put it up there with an old civic type R at 197 BHP or a merc SLK 230 at 197 BHP, so not be sniffed at.
there are a couple of supercharged JTS's about , autodelta made one which was around 220 BHP but its COSTLY!
any other weight saving stuff you can think of will always help, even taking the spare wheel out of the boot and going with a compressor and tyre seal kit.
I have in the past not been a big fan of the JTS having had a few issues with mine but I don't wish to criticize your choice of engine , and TBH if short journeys are your thing then why not see what's possible with what you have..?
good luck and let us know what you decide to do..