you can aim them slightly higher to get some more output. but the problem is the z is a low car already. thats the reason you dont get as much light as you want. you could upgrade the bulbs as well. our stock bulbs are 4200K Koito D2S bulbs.
if you want brighter, but same yellowish tint (4300K), you can get these from philips:
D2S: Philips 85122+ - HID Bulbs from The Retrofit Source Inc
if you want brighter, but a diamond/blue tint (5000K), you can get these from osram:
D2S: Osram Xenarc 66240 CBI - HID Bulbs from The Retrofit Source Inc
any of the bulbs will give you more output, about 3500 lumens. personally, from what ive seen our stock koito bulbs arent as bright as the philips, so id give you an "estimate" that the stock bulbs put out 3000 lumens or less. this is completely subjective of course