In theory, you can always learn more by continuing to study something. In practice, though, modern medicine has a pretty complete knowledge of smallpox. Humans have been studying the disease since before anyone even knew what a virus was. There's evidence that the Chinese were inoculating people for smallpox over a thousand years ago. And the first practical, widespread form of that vaccine dates back to the late 1700s. This was literally the very first virus ever treated with a vaccine. It's well-trodden ground, research-wise.
The problem is, this virus is highly contagious and relatively dangerous compared with other viruses. For variola major, the case fatality rate is typically 30–60%, which puts it among the worst communicable diseases out there, approaching the fatality rate of ebola, and far more contagious. With nearly a two-week average incubation period (and up to 17 days in the worst case), one minor screw-up could easily cause a very serious pandemic before enough vaccines could be produced and distributed.
So basically, you have to weigh the odds of an accidental release (which, with recent revelations about this stuff getting lost for decades, then turning up by accident, seems not so improbable) against the relatively small chance of learning anything new from it that can't also be learned from cowpox or other similar viruses. On the risk-reward curve, this seems to be so far towards the "pure risk" end that any reward would border on undeniable proof of divine intervention, which means the speculated rewards would have to be pretty darn amazing for it to be worth the risk.