+1 and as Digsy says stick with 18s
Got to agree on the colours here, although much prefer 19's on Zed's. They fill the arch much better and also save the need for spacers. I'm on 19" Nismos and the ride is perfect, can't tell difference from stock 18's - apart from much better grip ( wider and better tyres ).
The fact that they are 19" has no bearing on whether they need spacers or not - that's all about offset and width. An 18" with the right offset/wheel width combo will fill the arches much better than a 19" with crap offsets.
What Drewbie says about the ride is bang on though. The OEM Bridgestones have very stiff sidewalls which give a fairly unforgiving ride. When I went to 19" with Falkens the softer sidewalls cancelled out the effect of them being shallower and the ride was no worse. If you stick with an 18" wheel and a tyre with a softer sidewall you may even notice an improvement.
One word of warning though - 18" combos always look better lowered and unless you're prepared to pay for coilovers, lowering springs are likely to make the ride harsher.