I don't think an intake, exhaust and all that stuff which will cost just shy of 500$ total will make your car any faster at ALL. Plugs and wires may help if the old ones are toasted, if not again save your money. I'm sorry to be the bearer of bad news...
The brakes rotors could be warped. Also you could have built up pad residue on the rotors. The most common thing for me and my 900's have been incorrectly tightened lug nuts. If one is tighter than the other, and the lug nuts were not tightened in the correct star pattern order, you can get a bad brake shimmy.
Situation 1 requires new rotors. Eeuroparts is cheap and genuinesaab.com is right there too.
2 requires a couple of hard brake stands from 70 mph down to 10. DO NOT COME TO A STOP (70 to 0) as this is how the residue gets transferred to the rotors. This problem is endemic to EBC style pads, but its happened to me on OEM and the brake stands have solved the problem.
3 A 30$ craftsman bar type torque wrench is a good invesment, 83~ ft/lbs on the alloys and more on steelies. You can get away without a torque wrench, just tightening them all to an even amount but STAR pattern is what is key here. 83 lbs is NOT as much as you'd think either so dont over do it.