Quite. I should also like to point out that there are very few things you can do to an MP3 by editing it directly. In fact it pretty much comes down to just two; you can cut bits out of it (although not very accurately) and you can crudely increase or decrease its level - in rather large steps.
For the OP - I'll tell you what's a waste of time, since you mentioned it - editing MP3 files. Especially low bit rate ones. To do anything at all accurately to them you have to decode them back to an uncompressed format like wav - and when you re-encode them back to being an MP3 again, you've got it at an even lower quality that it was previously, because the masking will have been even more masked.
The original intention for MP3 files were that they would be a distribution format, not a working one. They were never intended for actual production purposes at all.
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