Well, to state the obvious, players like Strasburg and even Price don't come along very often. But, you (and Chuck) may have a point about a lack of "blue-chip" prospects being brought in by Wade/Heck. They have focused on athletic, up-the-middle players, and projectable HS pitchers each of the 3 drafts they've overseen, and those type players could pay off down the road but they're probably not going to be #1 starters or #4 hitters.
Also, while I'm sure 10 years from now we can look back and go "oh look, they passed over Joe McBigswing, the greatest 3B in baseball, when they could've picked him #10 in 2008;" there's always hindsight guys like that, but it's not like they've had the #1 or #2 overall pick and fucked up. Once you get down to #10 or #8 overall, there aren't too many "sure things" to be had. The draft is 90% crapshoot.
You're right. It's hard to find impact players from the college ranks, especially when you don't have a top-5 pick. This year might be an aberration, but generally guys like Tulowitzki, Longoria, Price, etc are going to be taken well before we get a crack at them. Instead, they've focused on athletes, which were almost non-existent in the system prior to Heck.
I think part of the discussion revolves around what defines an "impact" player. To me, an impact player is someone who changes the game with some aspect of their play. AE was an impact defensive player, Bourn is an impact CF and baserunner, Bagwell and Biggio were impact players in the mid-late 90's, etc. They could do things that other players couldn't. When you look at guys like Castro, I think he could develop into a good MLB catcher, but his skills are more solid across the board than game-changing.
When it comes to pitchers, I see an impact pitcher as a pitcher who can shut down the other team on any given night. In recent years, Oswalt, Lidge, and Wagner fit the bill. It's up in the air whether Lyles can become that kind of pitcher. The stuff doesn't seem to suggest it, but we'll see.
I'd say that Deshields could become an impact player if he develops like they plan. Folty has the stuff to become an impact pitcher. Outside of those two, I don't know how many other guys have the ability to be MLB regulars and stand out from the crowd. Not saying Heck has done a bad job, the depth is greatly improved, but we haven't have many home run picks (that we can tell), yet.