Firstly, hello and welcome
You actually answered your own question, the watches are identical aside from the bracelet on the 347. There is no mystery to this. The production numbers you quote are for one year only of manufacture, there are and will be yet more of both models. http://www.panerai.com/s_page.xpd?id_li ... goria=9035
Bracelet models can always have straps fitted as an option, though you'd need to buy a buckle too. Both are regular production watches so unlikely to become rare and sought after, and therefore will loose money initially like any luxury goods product. Over time, if you keep it long enough, regular price increases may see it become worth close to what it cost you, if it is still in pristine conditon.
If you are focussed on the 347, then try and blag a strap and buckle from the dealer as freebies, then you have the best of both worlds. If you plan a strap collection anyway, just buy the 321 and save some money.