1st. Chrome is 20 times easier to clean than POLISHED SILVER.. A painted Wheel (silver, white, ect) is easy to clean also, but you run the risk of Getting Nicks in your paint.
2nd. Having Larger Wheels and Less Tire Height, does not nessecerily give you more wheel gap. The goal is to maintain the same Overall Diameter of the Wheel and tire, thus giving you, an equal wheel gap.
3rd. 99% of the world agrees with me when I say Chrome is not ugly. Don't argue, it's pointless, every car manufactor offers chrome wheels for a reason.
4th. If you going for strictly looks, the larger the better. Do not enter a car show without 18" rims with high hopes.
5th. z-rated tires doesn't mean they have a smaller sidewall. All tires have a size that looks like this ###/##/##
The first three digit number is the Depth of the tire in Millimeters
The Second two digit number is the Sidewall height as a percentage of the first number.
The third number is the size of the rim that fits into the tire.
Thus my Wheel are 215/35/18 They are 215mm deep, 75.25 mm high (215 * .35), and I have an 18" wheel
Lastly this link will help you to determine what size Wheel And Tire you would like to purchase for your Civic.
http://www.2k1civic.com/stuff/tire_calc.cfm
I hope all this helps, and I hope I didn't step on too many toes.
If you want my Opinion, Buy some very large Chrome Rims, get a style that is not very common, and then save up and lower your car. People tend to notice wheel gap when you have huge wheels.