Hi njguitar.
I haven't found any guitars like yours for sale but we can still speculate about an approximate value. Here is a Ventura that was likely built around the same time as your guitar using similar construction techniques. These sellers are asking $400 which is pretty optimistic but it gives us a starting point.
http://www.ebay.com/itm/Rare-Vintage-La ... 3f236f2f5bThe positives of your guitar compared to the Ventura are that your guitar has split block inlays in the fretboard and some accent inlay in the bridge.
What I see as negatives of you guitar compared to the Ventura include the huge pickguard and the brand name. While the pickguard might be eye catching, it actually hurts the tone and sustain of the instrument since it interferes with the vibration of the top. The brand name issue is obvious, who has ever heard of a Tamaki. The guitar was probably built by a larger OEM guitar factory and then just branded Tamaki by a distributor, but it would take some work to figure out who actually built the instrument. It could have come from the same factory as the Ventura.
In terms of value, we have a Ventura for sale at $400 that hasn't sold. Couple that with the fact that you can buy lower end Epiphone, Takamine and Washburn 12 strings for between $400-$500 suggests to me $400 is a stretch. Assuming you want to sell the instrument on Craigslist, you might start the price at $300-$350 and see if anyone bites. Remember, you can always drop the price if you get an interested buyer.
Hope this helps,
sb