With everybody else rushing to push up their own stadiums while we struggled to go anywhere with our own for all these years, I expect the boost from the new stadium won't be as revolutionary as a lot of people here expect it to be. We will likely end up in about the same position relative to everyone else and all their own shiny new stadiums/stadium expansions (Etihad expansion, new Stamford Bridge, Anfield expansion + already existing Emirates and OT). Not saying it won't lead to increased spending, but a lot of the superiority we would formerly have enjoyed is now dissipating into mild competitive advantages at best and an even playing field with all the others at worst.
As for the initial bit of your post, like I said, the excuses for not spending during that period immediately after CL qualification were many and varied, including the 'Doing a Ridsdale' bit. But just don't try to paint that reality as 'backing a manager so hard that we're suffering for it now': that is patently not the case, and that is giving ENIC undue credit.