I just wanted to report back after picking up our 1.5 Sport over the weekend and to thank you all for your much appreciated advice!
We're very please with the car overall but admittedly there are a couple of small niggling things that could be a little better. In case anyone else is looking to make the jump from a MK1 Sport to the MK3 Sport here are a few of our thoughts.
Our initial thoughts comparing our MK1 Sport with the MK3 Sport:
Performance: MK3 >> MK1. There is definitely a step up on performance with low end torque being the most noticeable, making city driving much easier. We tried the ivtec a couple of times, its quite different to the ivtec in the old NA Civic Type-Rs where you feel a shove in the back when it kicks in. In the Jazz, it's a relatively smooth power delivery all the way to the red line, no noticeable change as vtec engages. Cornering is better in the MK3, the suspension is a tad stiffer and there seems to be slightly less roll in corners. The gear changes are very smooth except reverse which is sometimes difficult to engage - but as 1st is linked to Reverse, I have learnt that you just need to re-engage 1st then it will go into R very easily. The steering is very comfortable to use albeit less feedback than the MK1. I like the way it returns back to centre better than the MK1.
Economy: MK1 = MK3. We drove our 1.4 MK1 Sport about 130miles to collect the car and it averaged about 41mpg on the trip computer. Doing the same route back in the MK3, it showed an average of about 51mpg. So although this would make the MK3 a clear winner, there was a lot more traffic on the way there than on the way back and I don't fully believe the on board computer.
Features/Functionality: MK3 >>> MK1. There is no comparison here, the MK3 has far more toys than the MK1. We thought we'd miss the climate control but in reality it doesn't make much difference. We prefer the side mirrors of the MK1 as you can see a lot more whereas the MK3 is smaller and also narrows and droops down at the ends which makes visibility slightly worse. The indicator repeater lights in the mirrors seems a little dim in daylight, not sure if this will be an issue yet.
Practicality: MK1 > MK3. This is the one we were surprised about. Although there is very slightly less leg room in the back of the MK1 there is more headroom. We actually suspected this when we noticed the roof of the MK3 is lower than the MK1. But more importantly for us, the MK1 has a noticeably bigger boot than the MK3 (without considering the space under the boot floor). This will take a bit of getting used to as our daughter's stroller takes up quite a bit of space. The middle seat in back is also less comfortable in the MK3 as it is raised and has a very narrow seat for your bum but we don't use the middle seat very often. Also, we find that there is a lot more storage in the MK1 cabin than the MK3, mainly due to the under dash shelf and the small dash table in the MK1 but the MK3 makes up for some of it with the armrest storage and rear door card pockets.
Noise: MK1 = MK3. At very low speeds around town the MK3 quieter than the MK1. But on A-roads and motorways, I would say they are about the same. However there is very annoying whistling sound from the drivers side area at speeds above 40-50mph. Not sure where it is coming from, but I'm guessing it is wind noise, hopefully not a mechanical issue.
To conclude, we love the MK3 it is good improvement over the MK1 but it would have been nice to have a bigger boot, no wind noise and slightly more head room in the rear.
Here's a couple of photos on picking up the car: