no clues on Hawaii (yet) but i've been in/around Vegas
wining/dining/clubbing is what most folk do in Vegas but do visit the malls/boutiques.
Can do a fair amount of shopping even with a relatively lower sterling
the Grand Canyon's south rim is nearly 6 hours away so ya might wanna stay overnight when ya get there
dining options are rather limited in the Canyon village though
and if you're a REALLY hardcore outdoor enthusiast ya can even trek all the way down and up from the south side
another option is to head 2/3 hours north into Utah and come down to the Canyon from the north side
its native American territory so the tarmac is as bad as a motocross track but they have the Skywalk which hangs over the canyon so it might appeal to you. Southern Utah is also home to Zion Canyon National park and hwy 9 that heads east off the I-15 goes through some of the most beautiful red rock you'll ever see including a 1.1 mile long tunnel cut through the mountain range.
Perhaps after Zion Canyon, you can do the complete loop & visit Lake Powell in northern AZ (home of the grand canyon) while you're there, come down from the east side, visit the south face of the Grand Canyon and be back in Vegas within 24-72 hours
Near Vegas, you'll be fairly close to Lake Mead so feel free to venture out for some recreational jet skiing/boating with the your lady love. You could also go to Hoover Dam but its just an old place and rather played out IMO
if something else comes to mind i'll post up later