Great Coin!
Your coin is actually a very common 'error' coin seen in the 1956 - 1958 wheat series. The quality of the die's in that period, or the production lacked something. Filled letters, filled numbers and the BIE errors are more common than one might think. I have bags of filled letters/numbers, and dozens of the BIE errors.
I've seen coin sites offering the BIE coins for $5 - $7 a piece. That being said, trying to sell one to another collector, I think about a buck or two at most would be reasonable.
As for filled letters and numbers, I don't believe it adds much to the value of the coin. Maybe double the numismatic value (meaning.. if it were a $0.35 coin... now you might get $0.70 for it).
Below are some pics of examples that I have.
First is a BIE coin in XF to AU condition
Next is a coin that has both a BIE error, as well as a "Filled 5". Also in XF condition.
Finally, is a coin that has a "Filled B" in liberty.
