Guion wasn't that successful playing DT in a 4-3, so I wouldn't count on him being a good nose in a 3-4. Given his height and weight, I assumed he'd be a DE in base when we think the other team is going to run the ball. Without Pickett on the roster, we only have one NT and considering how we got worn out and owned by the run at the end of a bunch of important games last year, we need to have at least one other NT on the roster. Since Raji is probably gone next year, it'd be nice to have two, frankly. There are plenty of NTs who change the whole complexion of a defense (Wilfork, Ngata) so it's not a wasted pick at all.
Then again, maybe Boyd has put on thirty pounds and they're feeling fine about it. Who knows. The thing is, if we ended up totally unable to stop the run next year even when we know it's coming and we see Louis Nix playing for some other team and opposing offenses can't run the ball at all, we're going to feel dumb. A good dline makes the whole rest of the defense better. Having an all-world ball-hawk safety doesn't mean much if you give up four yards through the A gap every first and second down.