Good idea. However, your coding could use some work.
- Why on earth are you checking the player's level and running through 70 if-then-elses ten times every second? You could update the frame much more efficiently by watching the PLAYER_LEVEL_UP and PLAYER_UPDATE_XP events.
- The number of globals you're creating is cringe-worthy. Turn all those variables at the top of your file into locals.
- You don't need to create and update a variable just to tell you if the frame is visible. Use the existing frame:IsShown() API method.
May I suggest showing XP/hour and the estimated time to 70 based on current XP rate. Might be interesting. Could be depressing as well. Still would like to see it. Thanks.