I know nothing about civics. Below are some general options available to you.
You can get some high performance weber carbs. I see you have a dual chamber carb, but you can adapt that system to have two (2) dual chamber carbs - more power to be found there, I'd imagine - or you can go EFI (electronic fuel injection). I assume some of the later civics run on a swappable EFI system. I think the older Alfas had double carbs... Both of these options will greatly increase fuel consumption, though.
Now lets not kid ourselves, a catback exhaust on an NA 1.6 does little good. Your only advantage there is the fact that you'll be getting a new pipe and muffler, as opposed to the carbon clogged system you had before - but buying a new stock system has the same performance upgrade.
Is it a manual? Get yourself a shortshift kit, it may feel like more power, and definitely feel more responsive. Is it an auto? Get yourself a high torque stall converter. In both cases (but mainly the manual) you can lighten the flywheel (any reputable machining shop can do it) and it will climb the revs MUCH more quickly, and it will FEEL more powerful. Or if it's auto, convert it to manual...
Schrick offers performance camshafts for BMWs. Do you know of an aftermarket solution for performance cams for Hondas? It's possible. It will feel very responsive in the upper ranges, and definitely add a few kWs up there.
You can also get yourself a performance differential. I don't know what kinds are offered in civics, but generally a numerically lower differential will offer greater acceleration, at the expense of RPMs at high speed cruising. It will almost feel like a new beast - these can be called a poor man's supercharger.
Considering it's carbed, ECU upgrades are few - but check out if any chips are available. Though I doubt it.
One of the cheapest ways of improving power is losing weight - your car can go on a diet by removing things like rear seats, air con, or even more extreme - door trim, insulation and even dashboard. A 100kg reduction will give a difference you can feel.
That's what I can think of the moment, short of forced induction. I think one of the first things to do, before actually 'upping' the kWs, is checking your car is in optimum condition. DO a tune up, get new spark plugs, leads, change some gaskets, if you must, clean out the carby (you can do that yourself), do a compression test, change the oil, flush the coolant, do your brakes, and after you've done that - go nuts.