Many fans from other clubs are probably thinking the very same thing. However, the truth is that it isn't as simple or clear cut as that.
Bony for example cost £12m and came from the Dutch league, which is notorious for masking a players potential. Players can shine over there and come here and be atrocious; equally others can shine there and be very good. That's the problem: taking players who succeed in the Netherlands is a risk. Martinez had just signed for the club and we didn't have a significant transfer budget, thus went for players he knew or believed could rely on without a huge risk. A gamble could have paid off, but that's with hindsight. With regards to this summer? Well, we've spent a lot on a player who has relatively proven himself in league (for both us and WBA) and was wanted by a significant percentage of the fan base. Was it the right option? Could the money have been better spent? The jury is still out. However, I doubt we could have afforded both and simply saying we should have bought Bony doesn't take into consideration all of the above.
Tadic is much of the same for Bony. Well thought of in the Eredivisie, but that doesn't always mean much and was he a priority for us?
In hindsight he could have been a fantastic buy, yet hindsight is hindsight. It's easy to say afterwards we should have done this and that etc.
Song probably boiled down to his relatively well known poor attitude, possible wage demands and the fact that isn't a weak position for us.
It is easy to look at a successful transfer and remarks, "We should have gone for those! Our scouts are poor etc...".
The hard part is getting the right transfer in the first place and making it succeed. I'm not saying you're wrong by the way, or our scouts are perfect. I think our transfer dealings could be better, but it isn't as simple as some may wish it to be.