As NewVisitor says you need to realise the instances at the end to use the solidify.
Also for the letters to scale independently you have to use the position node in some way. The position node gives a different value for each letter.
To get a more wavy (less random) effect you can use a voronoi texture (setting randomness to 0) instead of the noise texture.
I have made a new version that is much closer to the original effect.
BouncingWavyText2.blend (170.8 KB)
Edit: I have changed the file a bit! Edit2 I used a noise texture before, I have corrected. Edit 3 Have changed the file again LOL