I have found that it's a dangerous prospect having beliefs like 'there is only upside with the stock sitting at $3'. Anything can happen.
Having said that, to answer your question about what I see as downside risk, here's what I see that could bring the stock lower in the near future (keep in mind that I'm long with an average around 3 bucks).
I would expect that around the earnings announcement they would give some sort of update on their recent activity. That update COULD include comments about not finding any gold or silver at all at the HMS Victory site. It COULD include a comment about needing to raise cash soon. It COULD include a comment about the Gairsoppa being a more difficult endeavor than they had been expecting due to its depth.
Of course, it COULD go the other way as well. They COULD say that it looks like their gold projections for the Victory were dead on or maybe even too conservative. If that's the case the stock soars. They could say they have found the Merchant Royal and inked a deal similar to the Gairsoppa deal in which case the stock soars.
Taking all that into account, the potential upside here definitely makes this stock worth owning around this price in my opinion. I view the Gairsoppa as a 'floor' under this stock since the story is known and recovery time is growing near.
So, I doubt this drops very far from here but knowing downside risks is still important for any investor in my opinion. As far as upside? It's really hard to say but I could certainly imagine a double from here if good news occurs.