The answer to both of these questions is possibly. I have discussed the overall factors that determine whether a coin is valuable or not(Date, mint mark, condition and precious metals content) in previous posts. A coin is not valuable based on it being certified alone. We often see certified coins that have no additional value, compared to a coin that is not certified. Coin certification can make your coin more marketable, based on the fact that some buyers have a higher comfort in coins that are independently evaluated and graded, rather than trust in their own ability to asses the coin. This is especially true when dealing with a rare coin. The difference in just one grade up or down can mean the diffidence of 10's of thousands of dollars, and sometimes more.
I think that grading levels the playing field to some degree when discussing values of your coin. I do however want to say that a coin that is graded ms65 is not necessarily gospel. In other words, grading companies make grading mistakes both up and down. So how do you know if you should grade your coin? I think it all depends on what you are doing. If you are a collector that is collecting a "type set" and you what a coin in each grade in your collection, then grading might be appropriate. However, if you are selling "raw" coins, it might not be advantageous to certify the coins. I have seen people pay $40 to certify a coin that is only worth $25. One caveat might be, if you have an error coin or a valuable variety coin, that requires an expert to distinguish the details of the coin, and that particular coin has exceptional value, then by all means get the coin certified.
On a little different note, storing certified coins definitely takes up more space. Not that this is a determining factor, but it creates a fair amount of bulk. The last thing to consider, and sometimes the most important, is the grading company itself and which one is best for what your are certifying. There are several grading companies to chose from, and it somewhat depends on the specific coin as well as the purpose for the grading. The company that grades the most largest amount of coins is PCGS(Professional Coin Grading Service), second is NGC(Numismatic Guarantee Corporation), and third is ANACS. There are some other smaller services as well. We would be happy to guide you on your options