First, take a look at this informative link, which I found pretty enlightening:
The Pansy Patrol - Info for the 3000GT / Stealth Community
To summarize, brake upgrades (i.e. bigger discs, grooves, drills, etc.) are mostly for heat dissipation to reduce brake fade when brakes are being used repeatedly. It is the tyres' contact patch area (and compound I guess) that are crucial in the actual slow-down of a vehicle once the wheels lock in case of a hard stop(or modulate at that level without locking, in the case of ABS).
Rear discs may help some, but on most Indian cars, esp. with front-wheel drive (viva?), this won't make a big difference. And it's probably not worth the hassle and price. This option makes sense if you're adding vast amounts of power to your car, i.e. with a turbo/supercharger or constant NOS. Which I don't gather is the case here.
The one option that IS worth trying though (in addition to bigger tyres), is upgrading the front-discs system and any parts thereof.
Hope that helps!