Only if you are completely sure that they are going to make it, or if you can get them on cheap. Spending that much money on them is bad, in any other circumstance.
If the 80m price is true, then you can add an extra bit and get Pogba, who is already a top player. Or you can even tempt Madrid for Kroos, who IMO is exactly what we need. Even 45m euros seems to much for me.
What Bayern does is a bit irrelevant IMO. They have this reputation of being the perfectly managed team (and they are very well managed), but they make a ton of errors like any other club. Maybe Sanches will work, maybe not, and I actually have no idea on that, but I can understand United's position for not wanting to spend all these money in a gamble, especially after all the money that we spent, we are still in a mess.
This summer window IMO should be all about quick fixes, and so proven players. Go for the likes of Griezmann, Ibra, Godin, Koke, Kroos and similar, and hope to get some of them. We have already a very good bunch of kids who can become top players, so for the moment we need to complement it with already top players (something that we are severely lacking on), because we cannot afford an another season or two like the last three seasons.