You said it yourself, Glaston, 6th highest wage bill in the prem. Now that would be acceptable had Spurs not finished 3rd (with a great chance of winning it) and 2nd in the prem for the last 2 years. The Spurs first eleven is one of the very best the prem has to offer, on par with Chelsea I would say, so why does their wage bill not reflect that? Don't give me the old "we just paid out for a new stadium" malarky, the players couldn't care less about that, you know it deep down. They wan't paying a salary reflecting their ability, evidence to this fact can be seen in Danny Rose's recent comments in the press, or Toby Alderweild refusing to accept a sub-par contract, or even Kyle Walker, sure an argument could be made that he left after falling out with Poch, but even you have stated that he left for the money. Spurs have been getting away with underpaying their players for to long, and although I disagree with the manner in which he presented it, Danny Rose's outburst was long overdue. Word it however you like, in whatever way makes you feel comfortable, but please don't deny the fact that Spurs underpay their players.
Wanyama worked out great but before he was signed, very few thought he good enough to represent the best team in England. Dier and Alli were practically unheard of before Spurs signed them. None of the 3 you mention would be considered high standard footballers before they were signed by Spurs. Which brings me to my next point.
Ross Barkely - good player, bags of potential, was once considered a future England star. Once upon a time. As of this moment, none of the other top 6 clubs are even remotely interested in in him because he has failed to kick on from that early form, his future as a possible England great is under threat due to this. That Spurs are the only top6 club wishing to sign him is a sign in itself. They simply are not capable of signing anything better.
In summary - In order to remain competitive and suitably challenged with worthy reinforcements, Spurs need to sign top players. Second rate pruchases/bargain hunting for that diamond in the rough simply won't cut it anymore. Plus they need to pay their current personnel a salary befitting their ability. Spurs, specifically Levy, needs to get his finger out before it falls down around him.