I see three main issues with that.
First of all, it'd be more find-the-cache than attack-the-base. There'd be no particular reason to build anything of note, and no reason to store anything anywhere except on your person or hidden in a pit in the middle of nowhere.
Secondly, not everyone's going to be on at the same time, which means a lot of the griefing, if there is any, would just involve dismantling their base and rooting around for their stash. You could potentially set a trap in there, but even that'd be of limited use if you weren't around to collect the spoils.
Third, how much gold you have is likely going to be a result of how much you play, not how well you've done. It's certainly not going to have a whole lot to do with how many other players you've killed, because unless you're extremely good at it (and they're carrying their stuff on them), you're just as likely to get ganked and lose your stuff as you are to take someone else's- and the time spent gearing up and searching for them is time you could have spent spelunking.
I do like the concept, but I think it'd just turn into a boring, nearly-featureless server where the point is to mine caves for no particular reason, and every now and then you get ambushed and killed or your secret cache disappears. I'd recommend something a bit more structured for a PvP server.