For some reason I thought you had gotten a pair of validus, sorry 
but yeah, even though humidity doesnt appear to be real important with these guys, I always worry about drafts and keeping specific temps and such. Thats the only reason I harp on sealing it up. I am more of a teiid person myself, and I know that although tegus will tolerate a really wide variety of humidity, that they will do best in a higher humidity, even when their environment doesnt dictate it. So I always make sure I can control those values as efficiently as possible.
As for the digging, to me its all about just giving them the options to do so. Even if your validus never uses it, at least she has the option. Also, allowing them to burrow through a natural dirt substrate seems to keep their scales glossy. I believe it was Ingo Kober who on another forum mentioned that he noticed this in his G. flavigularis (or maybe it was a nigrolineatus, I dont remember) but after seeing this I prompted a friend of mine to try it with his nigrolineatus, and he had similar results-while they will get dirty, their scales appear more glossy, and they seem to really enjoy the tunnels they have made. But of course, thats just my opinion. 
Paul