The restrictor is put inside the clutch line to slow the movement of the fluid inside the line. So, when you push the pedal, it takes a tad longer than you would think to move the clutch actuator. The bottom line here is that when you try to shift quickly, the car may fight you when you try to enter the next gear.
As far as the heavy clutch, that is usually caused by the pressure plate of the clutch. I wonder what kind of clutch the last owner had installed? I'll tell you this, the factory clutch was very mushy. No resistance at all and it was terrible at launches. I would say that if you have pressed the clutch pedal in other stock DSMs and yours is still stiffer, then I would belive that your clutch kit is not a factory replacement.
The one thing that will help you reduce the pedal effort is to replace the clutch line with a steel braided line.
When you do this, remove the restrictor in the opening where the line attaches at the actuator. The line and the actuator removal will make a world of difference.
BTW, make sure to bleed the clutch line and refill the clutch's master cylinder.
Go here to check out more info on the restrictor removal.
http://www.vfaq.com/FAQlocator-drivetrain.html
Here's a link to a place where you can get the 2G clutch line. They aren't very expensive.
http://www.turbotrix.com/parts/driveline.shtml
Good luck.