It looks like you have plenty of room to add depth to your hedge.

For info on a multiple-layer "screen," see the inspirational photo linked at spazzycat_1's first post on this old thread, and read all her posts on that thread for more details about her screen. [She's not too far from you (a bit south), and a zone or two warmer.]
http://forums2.gardenweb.com/forums/load/design/msg0415211512336.html

To find that thread, I searched her user name and "screen." If you'd like to check other posts, here is that Google search:
http://www.google.com/#sclient=psy&hl=en&q=spazzycat_1+screen&aq=f&aqi=&aql=&oq=&gs_rfai=&pbx=1&fp=6f32b8af52b7e0b8

Keep in mind that the maximum height of Leyland cypresses is unknown -- the oldest ones are still growing at 130'.

I have a Great Wall of Leyland Cypress, planted by my southern neighbor maybe 15-20 years ago. They are varying heights, depending on where other trees are (or were) on both sides of the property line. Most are probably in the 50-60' range. Because the Wall is so tall and so solid, the southern half of my property gets no sun for months in the depths of winter. Snow never melts. The ground never thaws.

If you plant a tall inner row in front of your Leylands, consider removing at least some of the Leylands when the second layer of hedge is 6 or 8' high, and replacing them with something that's not so opaque or so tall. Particularly if your Leylands are along your northern or southern property line.

Adding dogwood,maple,conifer,azalea...maybe work,you select.
{{gwi:48402}}

Thanks those are beautiful pictures. Many ideas to inspire... thanks!