What ones to you are worth buying if you already own the original record? Blind Guardian, Iced Earth, Megadeth, Iron Maiden, Death, and countless others have reissued and remastered old albums, updating the sound quality and/or adding rarities and b-sides.

also, Im wonder how the meshuggah reissues (the albums ending in reloaded) are compared to the originals. Are they just reissued with bonuses or are they remastered (to the point where they sound different or better than the original pressings)

I think we already have such tread somewhere
But generaly i prefere orginals because many cases 90% what I have seen re relise album artwork suck big balls, but many cases 95% why you need buy such is bonus tracks, demo tracks, live recores, IMO 70% re relises has soem bonus materaial, one more extra songs so ... its worth to buy, if only they wont mess whit artwork