If your 1.3 if running fine and in good condition, keep it. Take the money you'd use for an engine swap and add some extras to your 1.3 that will carry over to a 1.6 down the road.
If your engine is on its last leg though and you are considering a rebuild, then the 1.6 makes sense. Pretty much most of the 1.6 kits we sell are to guys who have looked at the cost/benefit of rebuilding their 1.3. You spend quite a sum of money and at the end of it all you still only have a stock Suzuki engine. For not much more than a rebuild you can drop the 1.6 in which will net you noticeable gains (assuming the engine you swap in isn't in poor condition).