econman,
You have to take the original with you, since they do ask you to bring all original documents. I would play it safe and take another translated notorized copy. They might not even ask for it. But if they do and you don't have one, it may not be a nice siutation to be in.
It's true that they sent you a generic letter, but that could be because they are used to sending out such letters.
In my case, I had sent them a copy of the b.c., an original translated notorized copy and a letter from the translator saying the translation is correct and he is well versed in both the languages.
if you have lived with your spouse for more than 6 months, your spouse can use your income by filling in supplement A (864A)
I am not 100% sure on this you might want to read the form again and check with someone else.
All the best for your AOS interview. Good Luck.
Regards,
AmIinTrouble