Ahh, Harrah's buffet. For the value it's by far my favorite Vegas buffet. Three options:
MRB has a coupon for $5 off the buffet. There's also a BOGO for Harrah's Improv though you could probably get that ticket at the half-priced ticket booth. If you think you might do a couple more CET shows, you may just want to get the 48-hour pass for $99.
ACG also has a coupon for $5 off the buffet, and it's good for up to four people.
Lastly, SOMETIMES there are showgirls passing out $5 off buffet and/or Mac King coupons in the Carnival Court area or on the south side entrance of the Flamingo. Sometimes the coupons are for the Flamingo buffet. They are not always there -- seem to be off hours though during the day -- so if a show girl is there and doesn't have a Harrah's buffet coupon, sometimes I just ask when they will. I've also been told you can ask for one at the HARRAH's Total Rewards desk, though I've never tried it.
One of my first "to dos" when I get to Vegas is to get as many of those coupons as I can as I'm often in Vegas for long trips.
Good luck!