I'd love for him to succeed at Spurs. He has shown glimpses of genuine quality and has undeniable determination and a great work-rate. He really wants to do better and tries his hardest. On top of all that, he's still very young, so he could yet find another level. But at the same time... we're coming to the end of his second season at the club now, and he's just not demonstrated the consistent quality we need from a creative attacking player. Going into next season with Lamela in the first eleven is a big risk; based on what we've seen of him this season. He's not yet good enough for where we want to be in my view.
His saving grace, in my eyes, is that there is a whole host of players ahead of him in the queue for the exit door. I'd be very surprised if any of the following players are still at the club next year... Adebayor, Capoue, Kaboul, Paulinho, Chiriches. And I also suspect Dembele, Townsend and Stambouli might not be in Poch's plans.
So keeping Lamela as a squad / bench player would make perfect sense. If he finally fulfils his potential and it happens at Spurs, then everyone's happy and he can step up into the first team squad and rip premiership defences apart like we all hoped he would. In the meantime, he's certainly good enough to play our group matches in the Europa League and the early rounds of the cups - so he will get game time and the opportunity to progress.
For now though, if we continue to play 4-2-3-1, and if Eriksen and Chadli remain two of that "3", then we need a new player ahead of Lamela as the third (and no, I don't think it should be Townsend). Assuming this season wasn't a one-off from Kane, he's too good a striker not to provide with top class support.