Thank you for your question...I've just joined Trulia as a real estate Professional and would be happy to answer your question. First, there is no exact dollar figure on how the 6 lane Hwy will affect your value. What you need to realize is, there will be less buyers interested in a home that is near or backing to a busy street. Most often when I'm sitting with my buyer clients and looking at homes on the MLS, I will mention that this home backs to a busy street and the buyer will say, "I'm not interested" and we move onto the next home on our list. So, that said, the pricing of your home needs to encourage buyers to see your home. Which means your home has to be priced very competitively against the comparable homes on the market.
To answer your other question, about updating... it depends. If you price your home knowing that it needs updating, you will attract buyers interested in a lower price and updating themselves. On the other hand, if you update and price higher (since you did put the money into it), there is no guarantee that 1) the prospective buyer will like your choices and 2) the buyer will "reinburse" you for the money you put into it. If you are going to live in your home for another 10 years and would enjoy your updates, then I'd say absolutely, go for it. More than likely, the mechanicals will fail and need replacing in those 10 years. But if you are not going to sell soon, there is no reason to "fix what's not broken."
Hope that helps.
Michelle Price, ABR, CRS, CHMS