Card Identification Forum

In coins errors like this are rare and usually increase the value of a coin. Does this hold true for cards? A dealer once told me it was worthless but I always thought it was cool so I kept it.

Coins and cards are very different when it comes to production errors.  Production errors on cards are pretty common, whereas govt mints usually have much better QC and they don't get out to the public.  That said, if you find the right Mussina collector, they'd likely be interested at a significant multiple of what that card usually goes for and you could get a buck or two instead of a dime. 

Just for comparison, I sold an '89 Topps Roger Clemens with a Jeff Ballard back on Ebay for $1.25 in an auction (free shipping).