I have a Focus 1.6 Ti-Vct also with 30k on the clock and full service history.
I get what you mean about the engine noise my engine has a bit of a raspy note when the engine is under load. Like a rushing air sound that is distinctive on a turbo'ed motor.
Also my temp gauge will sit a cold until I drive up a few streets then it just shoots up to the half way mark and sticks there! Also I have came out to my car an hour or two later after a drive and it heats up instantly!
Hi mate the ST has an extra 5th cylinder which gives it a characteristic engine / exhaust note. You will be hard pushed getting that noise out of a 1.6 4 cylinder.
Ford spend a lot of time developing the sound symphoser on the mk3 ST to try and get that sound back as the new ST engine is back to a 4 cylinder.
Exhausts wise there are a few people on here that have fitted custom dual exit exhausts which will hopefully help you out. You cant fit an ST exhaust due to the interfering spare tyre well found on non ST models.