Tweening the z-elevation works well for scaling text and spritefont:
This can be done much easier now with the scene graph. Add text as a child to the sprite, and it will scale with the parent.
For any future travellers looking for an easy way to do this, I've attached an edited version of mekonbekon's events with dop2000's mentioned method (set text as a child of a sprite, and tweening the scale of that sprite)
As far as I know, scaling with 'scale' works for most things but doesn't for 9patch for example, so I scaled the 'size' instead.
PS. In my case, I wanted a number(text object) that represents the amount of collectibles collected to quickly increase in size/scale before returning back to normal.
Here's a screenshot of what I did: (sprite is invisible)