I've experimented a little with this myself. So far, it seems that the best thing to do is just remove the big 'box', and leave the rest. Taking more away tends to make the engine lose bottom-end because of too much air getting in. Remember that N/A engines like to be 'tuned', or have a certain balance in regard to intake/exhaust flow.
Anyway..... I felt that removing the big box smoothed out the mid to upper end, while retaining the low end. Gives a nice growl at WOT also. Gas mileage didn't seem to be effected much either - still get 26-28mpg.
Plus, it's a 'free' mod!