in general, ms67 is worth a godawful amount more than ms63 or ms64.
triple the value or (much) more, depending on rarity of coin (*maybe how old the coin is would be more accurate... very few coins pre-1960 or 1970 will be ms67... before people started getting stuff just as 'collector's items'.... think of like the baseball card price crash)......
ed: ANACS is a 2nd tier grading service, for a coin of significant value, i'd get it graded by PCGS or NGC. i don't really know what these are though? and i guess just a niche market, instead of coin collectors as a whole?
Regarding ANACS, I really had no idea who to send the coins to. I found them as the first grading service I came across in a google search, contacted them to see if they would grade Casascius coins, and the vice president came back and told me they would. I probably won't have this coin regraded, but I'll keep that in mind for any coins I have graded in the future. Good to know.
Casascius coins: https://www.casascius.com/