Quentin Groves looks like a much better passrusher than anyone we have now; if we wait until the second round, he may be gone, and we will have another season without any passrushing threat. On, the other hand, when I look at the receivers who will be available at 29, they don't seem any better than the receivers who will be there at 39. It doesn't make sense to me to choose, say, Mario Manningham at 29 when we could draft, say, Andre Caldwell at 39. If we draft a WR, at any point in this draft, he will be unproven and have a high bust potential. That's just the draft we have here.
The Niners had a lousy offense last year. Their defense was marginally better, but that doesn't mean drafting a defensive player or two wouldn't make a huge difference.