In general, you'll have shorter tyre sidewalls with bigger rims, so handling should be better, possibly at the expense of a little ride comfort. No reason 18s should scrub any more than 17s with correct tyre choice, lowered or otherwise.
You also need to consider offset, ie where the centre of the wheel is on its rolling axis relative to the hub bolt face. Lower offsets stick out more, while higher offsets are less likely to clear big brakes (in general)
Bear in mind some larger rims weigh a lot more. That's more weight for the engine to spin, blunting performance.
19" OZ Ultraleggeras (lit: "Ultra-Light") on the other hand...