I just, this morning, threw down $175.00 on two new tires for my 16's. If you'll remember, I haven't had them all that long. Sport tires wear fast.. and you'll only be able to buy sport tires for 18's with a low enough profile... and those tires are going to cost significantly more than mine did. 18's are not a one time investment... they're a big peice of bling you gotta protect and polish often (aka, a chore).
I was going to have to replace them soon anyway, but I went out this morning and discovered that one of them was flat.. I found the nail a few minutes later :x Now I've got 16's on the front (rotated up from the rear) and 13" steelies with snow tires on the rear.

Tirerack should have my tires to me by Wednesday, and I should be back to 16's all around by next weekend. :? I had some plans to go driving on some windy-ass backroads against my friend's WRX tomorrow too
If you really want 18s, that bad, go for it. Like Tito, I reccomend you find a nice used GT or LX-E to swap your suspension onto. Since your not into upgrades for the performance aspect, then you're kinda throwin your money down the drain trying to make the escort look good. IMHO.