If the light is just right, a view from just about anywhere can be quite good. For instance, here's a look from Dickey Ridge, right as Skyline Drive starts to climb:
http://www.flickr.com/photos/kevinborland/2282927843/

It's a short hike to Hogback Overlook
http://www.flickr.com/photos/itinerant_wanderer/4093425455/

For maximum flexibility I recommend Big Meadows Lodge, even though it's not near the north part of the Park. The views are pretty good
http://www.flickr.com/photos/47726343@N00/2713729182/
and, even if the weather or light are lousy, you can easily find a romantic spot in the lodge rec room
http://0.tqn.com/d/usparks/1/0/Y/2/-/-/Shenandoah-7.jpg
http://www.flickr.com/photos/8818379@N05/2798446088/

And, if the couple decides this lodge IS a romantic spot, they can make it their next stop after the wedding, for a place like this
http://0.tqn.com/d/usparks/1/0/_/2/-/-/Shenandoah-9.jpg

I think the best view in the park is Hawksbill Gap Loop Trail. This is over your 1/2 mile though, but is a super nice hike and isn't much over a mile if I remember correctly. There are plenty of great overlooks that would be nice.

We recently visited Monticello(Thomas Jefferson's place). Maybe even in the gardens area there would be good?

I second the Hawksbill recommendation. There's an overlook platform, probably dating to CCC days, at the top of Hawksbill near Milepost 45 (4051 ft -- highest peak in park). One of the prettiest spots in the park, and a relatively easy hike adjacent to the Appalachina Trial. Farther south -- near Milepost 85 -- is Blackrock, also adjacent to the Appalachina Trail. It's is equally beautiful (IMO) but a little more remote and less crowded on typical summer or fall weekends. Good luck!

Typing much too fast -- I meant Appalachian Trail