You guys are forgetting the still ongoing loudness war (even Ben who recently posted about it...).
Unfortunately the re-releases are often spoiled at the final mastering stage, in which they are compressed as much as possible to make them louder.
The original releases (if they are old enough) usually have a lot more dynamic variation. If they have problems with equalization that can be corrected by applying some EQ on playback. For instance, some releases from 80s have slightly thin sound because the equalization was not properly corrected for the CD release.
People often get fooled because the louder and compressed remastered versions may initially sound "better" when they are briefly compared with the more dynamic first generation CD releases. The real truth becomes apparent if the loudness difference is corrected by adjusting the playback volume level (the replay gain system can do this) and the releases are compared on a high quality playback system.
Naturally there are exceptions to this. Sometimes the first generation releases were really bad and a remastered version fixes various problems.
Personally, I would carefully consider if the additional bonus tracks are so important. Sometimes it is possible to find many of the bonus tracks in separate "rarities", "b-sides", etc releases which don't contain the original album tracks.
Though, I have found that the compressed versions are good for listening in a noisy car...