I'm afraid that shredding is a little beyond playing a couple of scales really fast. To simply play scale patterns frontwards or backwards takes very little effort and the ability to play fast is a good tool to have but it is more important to be clean and articulate. Someone with decent speed and excellent articulation is always going to sound faster than someone who is incredibly fast but sloppy. The other thing is that if you only practice a couple of scales/modes, what will you do if you are jamming with someone and they switch to something totally outside of your grasp? Say you are jamming over a nice min/min/dom7th progression and your ripping out the harmonic minor, phrygian, etc scales that you practiced over and over but then everyone switches over to ii - V - I jazz progression or a i-iv-v blues progression but you haven't learned or practiced any other modes like dorian, pentatonic, blues, etc. Now you are stuck in a room full of people that are having fun jamming but every time you try to jump into the jam your licks don't fit whatsoever. You can play'em really fast but no matter how fast you play in the wrong key or wrong mode it's still going to sound really bad. That is why it's important to learn your theory and to practice theory application. At least that's one reason. A lot of people don't realize that improvisation is very seldom improvised. It's based on having a knowledge of what to play where and understanding what works with what and over what. Time signatures, modes, cadences (change overs), transitioning, articulation, etc are all very important. You should build up as many different skills and as much musical knowledge as possible so that you have the ability to play what you want or write what you want at will. I know I've been kind of pigeon holed as a shred guitarist over the years but what a lot of people are really shocked by when jamming with me and whatnot is that I can also play blues, jazz, classical, country, fusion,etc. and I honestly like seeing the look on there faces when I whip out some Johnny Cash or Beethoven in the middle of a jam session.LOL I would also recommend learning to sing both lead and harmony as most bands want someone who can at the very least sing harmony, which brings me back to the theory side of things. It's hard to do harmonies if you don't understand 3rd, 4ths, 5ths and whatnot (3rds being the most common I would say). Practice hard and you will see results, practice little and you will see little results.