Dempo- Nothing's a waste of time... graffiti's one big learning experience. You have a lot of extensions on the bottom that don't really help the piece, and the one on the top right of the V is the same deal. Keep working on those letters to build structure, and then try adding extensions that compliment the style and flow of the piece.
Pover- Keep your bar widths even, or at least fairly even. Although there are times and places where varying the bar width works, you're not quite there yet. Also, your 3D needs some serious help. What happened in the gap towards the bottom of the P? And at the top of the P you made a drop shadow instead... Check out the good threads on this site to get an idea of how 3D should work.