Every appointment is speculative. Van Gaal would still be a gamble. He has the potential to let his reputation come before his knowledge and could lose the dressing room very easily. The bloke can be a complete nutcase at times, and as I've already pointed out, his track record over the last decade is not as impressive as some would make you believe. He has a history of fall-outs, and if there is any club he will do that at, it's ours.
AVB would have never been Barca coach just because he got Tottenham Hotspur to 4th place. His brand of football would not have been allowed at that club, and he would not be given time to grow into the roll, he'd need to hit the ground running.
I also don't believe he was close to joining PSG. That was mere speculation in the papers if I recall. Typical summer transfer window stuff.
Interesting point at the end you make - "give us someone who can win...it will mean the club is in a better spot and more attractive". Harry delivered on both these fronts, yet we have gone backwards since his departure. He left us in a good position, with a good reputation after our run in the Champions League. Since then we've been Europa League regulars and still haven't got close to winning that.