Some people just have more athletic ability than others. No matter how hard I train, I doubt I could ever be fast. What you can achieve is 95% engine, not the bike. If you have knobby tires, slicks can help reduce rolling resistance. Lighter wheels probably have the biggest impact. It takes a lot of energy to get heavy rims spinning and lighter wheels help here. If you think about the weight of a bike, think again. Combine the weight of you plus the bike. Dropping 10 pounds out of 160 isn't that much percentage wise. And a lighter bike doesn't cut down the wind resistance. Drop bars put you in a position where you have a smaller profile when you ride and hence lower wind resistance.

If you want to get faster with what you have, I recommend more miles. Longer rides improve endurance. Intervals and hills also help as does riding regularly. The interwebz can probably help you find a training regimen if you wish to invest in cycling.