What are you trying to protect from what?
Sandboxie, as I understand it, protects the rest of your system from rogue applications. This could be a backdoor in a legit program, or a compromised program (as in a web browser after a malicious site), etc. Those rogue applications won't be able to access your wallet.
However, unless you're planning to run *every application on your system* in sandboxie, I'm not sure what gains you'd have.
It doesn't appear that you can use it to protect a program from other programs - so something running in sandboxie may not be able to touch other system resources, but other system resources could likely still touch it.
I'm a bit confused - if you've got a use case in mind, go ahead & explain it & I can take a look...