One of the best signings Houllier made many moons back was Marcus Babbel, who, like Schweinsteiger, was a World class footballer in his position. And like Bastian, was at the back end of a great career. But what made Marcus so important, aside from the quality he brought on the park, was what his experience brought off it. His stellar German professionalism rubbed off on everyone, and although he wasn't the captain, he become one of a few veteran captains on and off the pitch that helped the younger players develop immeasurably. And although his stint was short (4 years); he was integral to our second treble winning team his second season in 2001 and the side that ran Arsenal so close for the league the year after.
And that's where I think you'll gain most with Bastian like Mad alluded to. An experienced leader. On and off the park. At 30 and on the downside of a great career, this isn't a 'statement' to the big boys in Europe zz. Can't seem them seeing it as that at all. But it is a fantastic veteran presence who should help Van Gaal immeasurably. On and off the field.
And like Babbel, I think it will be more years 2 and 3 when you really start feeling it. Utd fans will doubtless disagree, particularly among the current euphoria, but your still a good ways shy of challenging Chelsea, let alone Europe. (Your realistic aim there should to get out the groups. Which is no given at all. Anything above and beyond that would be a bonus.). You're adding some real good building blocks, but there's still a long way to go as I currently type to get back to where you doubtless believe you should be.
The battle for the Champions League places should be a good one this year.