There's probably not a lot that you will find about the Artley Symphony model flute. As you noted, Artley didn't keep good records of the serial numbers prior to 1952 and serial number 10000. Around then Artley was making a couple thousand flutes each year. Since you bought yours in 1948, a good guess would be that it was made around 1947 or 1948.
There were a couple of variations on the Artley Symphony flute. Some had a silver headjoint, some had a silver plated headjoint, all of them had silver plated body and keys. If it's not engraved or marked "Silver" on the headjoint, it is almost certainly silver plated.
I have a slightly newer Artley Symphony (1960s era) that I bought on eBay a few years ago and I paid $20 for it. Unless it is playable and in pristine, like-new condition, it is probably not worth a lot more. At the high end they occasionally sell for $100 or if completely rebuilt, maybe $200. The Artley Symphony is not a bad flute. In good condition, they play OK but not great - good for a beginner. Unfortunately, there are a lot of old Artley flutes out there and they are not in high demand so the prices remain fairly low. See this eAby list of Artley Symphony flutes that have SOLD recently:
http://www.ebay.com/sch/i.html?_from=R4 ... ld=1&rt=nc
Since you said it has not been played for 59 years, it will probably need a complete repad to put it in playing condition. That would likely cost more than the flute is currently worth.