Hello Killbox,
Looking through your list, I'd have to ask you to consider what your priorities are -- performance or looks. Sometimes you can have both, but sometimes, the mod only fits one purpose or the other. In fact, some of the mods you listed have the potential to make the car "worse" than stock.
- 15" to 17" wheels and tires
Personally, I would be against this one. IMO, the DE Mazda2 is made with the 15" wheels and tires in mind. A 17", IMO, forces you to use a tire that has too low an aspect ratio, and that makes for an rough and bumpy ride. I dunno how the roads are in Malaysia, but the lower aspect ratio tire will also make your wheels more prone to pothole damage. Also, a 17" wheel and tire setup will be heavier than an equally wide 15" wheel and tire setup by quite a bit, and you will be sacrificing performance with the 17" wheel upgrade. Given the meager power that our cars have, I do not think the performance hit will go unnoticed.
As far as wheels upgrades are concerned, I'd recommend you to look through other owner's cars, and see what a good 15x7 or 15x7.5 wheel would look with some 205/50/15 tires. This +0 setup is still a totally worthwhile upgrade since you are moving to wider tires (ie. more grip) that has a lower, but still perfectly streetable aspect ratio (ie. sharper and faster steering response). The 205/50/15 tire size is also a very popular performance tire size, so there'll be no shortage of high performance rubber for you to choose from.
- braces and anti-roll bars
With our cars being a typical small displacement FWD, the front heavy weight bias along with the factory suspension setup means our cars are designed to understeer when you try to do any serious performance driving in it. Generally speaking, when your car is plowing (ie. understeering), it is no fun to drive, although it is probably a bit safer than having the car oversteer. From a performance perspective, you'd really want to stiffen up the rear and/or give your front wheels a bit more negative camber to reduce / eliminate that built-in understeer. If you do any / all of the braces and anti-roll bars that you mentioned above, you are only going to make the car understeer even more, and your car will be no fun at all to drive -- primarily because it wouldn't turn well at all. So do it one step at a time -- I'd opt for some camber bolts and a precision alignment for the front to max out your front (negative) camber first. Chances are, that mod should make your car neutral enough.
- power
Depending on how extensive the exhaust you are looking at, it may or may not bring any performance benefits. But it will likely give you a lot more noise, and possibly some very annoying drone as well. If you are interested in a real power upgrade (our cars sorely needs one), I would highly recommend an ECU tune from Dynotronics -- do a search on the forum for it, and you can read how happy the owners are with the ECU tune. The power difference and drivibility is night and day.
- suspension work
I would highly recommend some suspension mods to get the most out of our cars. In stock form, the car rides too high, and the springs are far too soft for any performance driving -- but it is plenty comfortable though. There are lots of popular options available, but I have yet to finish my own research into this topic, so I'm afraid I can't make you any recommendations.
- crank pulley
Generally speaking, I would not do any crank or accessory pulley mods on a street car unless I have completely exhausted all my power upgrade options. OEM crank pulleys generally have harmonic dampers built into itself, and that serves to dramatically improve NVH (noise, vibration, harshness) characters of the car/engine. Aftermarket pulleys tend to not have this. In extreme cases, the lack of harmonic dampers in the aftermarket crank pulleys might cause excessive NVH issues that damage your engine. Aftermarket pulleys may also underdrive the accessory components that depend on it -- ie. your alternator may not produce enough charge because it is being driven slower (by the aftermarket accessory pulley), so your battery may be overtaxed and wear out faster.
I hope I didn't sound like a party pooper. As an old fart, I can safely say that I have been in similar shoes as you have, and made many of the same mistakes that you have mentioned here.
