I don't have any hard data to back this up, which is why I'm just throwing this out there in a short fanpost. But I was clicking through Baseball America's top 10 prospect lists just now, and it struck me that there doesn't seem to be an abundance of top-flight 1B prospects out there these days. Here's a list of every guy in baseball whose primary position is 1B and who's ranked in his organization's top five.
Yonder Alonso, Reds #3 (since traded to Padres)
Jonathan Singleton, Astros #1
Anthony Rizzo, Padres #1 (since traded to Cubs)
Tommy Joseph, Giants #2
And that's it so far. BA isn't done ranking all the teams yet, but I looked at Sickels' lists for the as-yet-unranked teams and it looks like the only guys who might get added to the list are Chris Parmelee of the Twins and C.J. Cron of the Angels. That seems like an unusually short list. My impression is that there's usually a disproportionate number of 1B on these lists, since that's where you put the guys who are only good at offense.
Two caveats: (1) 1B is the easiest position on the field, so some guys move there after reaching the majors -- for example, Miguel Cabrera and Albert Pujols. (2) There are a number of young guys out there who are still "prospects" of a sort but aren't eligible for these lists because they've hit rookie eligibility -- Eric Hosmer, Justin Smoak, even Freddie Freeman. Still, it seems to me that even in relative terms, the list of 1B prospects is shorter than usual. Maybe that vague impression is wrong -- YMMV. But if it isn't wrong, that could mean that 1B prospects and young 1B are more valuable today than they usually are.