You accuse others of making baseless claims while bringing up the myth of Kagawa winning the award of the best Bundesliga player of the season? He did not win it once, let alone twice.
The other problem with your post is that aside from RvP, Kagawa and Mata all players you listed were either promising talents or came from significantly smaller clubs. Even RvP and Kagawa made a step up by joining United and the transfers were under favourable circumstances for United.
Kagawa made it clear quite early that his ultimate goal was to play in the EPL and especially the most popular United given the massive standing of the league in Japan.
RvP is a world class striker, but also injury prone and was for his age and contract situation a quite costly transfer.
That leaves Mata, a player with undisputed class, but also a player who was driven out of the team by Mourinho because he did not fit the latter´s tactical plan. He was also expensive.
Now, in the cases of Vidal, Kroos and Reus you have no favourable circumstances. Vidal is Juventus´ star player, payed as such and has already signed a new contract in December. Kroos plays for a club, which is not only at least equal in pretty much every aspect to United but also has a history of not selling players they don´t want to. Kroos himself has also already confirmed of playing for Munich next season.
Regarding Reus, I don´t see any reason for himself or Dortmund to transfer in the Summer, unless you make an offer both parties can´t refuse, which means a huge transfer fee, a big salary and quite a bit of a signing fee for the player/agent. That could summarize to around 80 Mil. € quite easily, a sum I don´t see you guys paying. The guy can leave for a bargain (in relation to what he brings to the table) in 2015. I can see nearly every European elite club lining up then and be ready to pay the 35 Mil. € towards Dortmund. Everything on top of that (a signing fee of 10+ Mil.€ is not unrealistic) will go directly into Reus´ own pocket. There is no reason to force an earlier move, especially when he will be unable to play in the competition which he regards as the most important in that one season.