You want a rear anti-rool bar to increase turn in, and make the back more communicative.
On both my Suzuki Ignis and Celica GT4 I have fitted a White Line Flat Out rear ant roll bar, made both car much more pointed, with much less understeer, though the Ignis is not an understeery car as standard, though had no rear anti-roll bar as standard. The Celica's bar is thicker than standard and adjustable as well makes front end very pointy and removes understeer, you can also make a rear wheel cock up as front end grips with much more verve than before.
The integrale also has front and rear anti roll bars, again most people uprate the rear leaving the front well alone.
I know of someone who has made a rear anti roll bar, its still being assessed but IIRC it came off a readily available car in scrap yards and looks very neat and i believe will make a brilliant upgrade to any cento.
Uprating the front will only cause it too corner flatter bu with more understeer, think of it as s spring across the car.
Removing the anti-roll bar will make it roll more, and lean even more in corners, unless suitable hard springs are employed, but both cars mentioned are track orientated cars with hard track set ups. Just drive a Cento 899cc and see what they are like with no anti-roll bar.