I actually work at a Hampton in Memphis, although not at the downtown location. $120 on a weekend is a steal for the downtown Hampton. It is almost always sold out on weekends, and has a great location.

As for upgrades, I believe that Hampton Inn and Suite locations DO upgrade gold and diamonds to suites based on availablility, but if they are sold out, I'm not sure your chances. Might do you good to call ahead of time (ask for Aisha -she's great) and request an upgrade?

Keep in mind most other hotels in downtown are easily $150+ on weekends.