A new stadium is a Pandora's box for any club. When we built Emirates, a huge proportion of the revenue from the stadium was designed to come from corporate supporters. You can't expect 60,000 'cheap' tickets to meet the revenue demands of a new build and gate profit increases, even if Spurs do secure some local development funding for the development.
It's no secret that clubs like Arsenal have attracted some fairweather fans. A combination of expected success, a big new stadium and some less than die hard fans who expect to be entertained before they start cheering on the team. Also you have to remember that in a new build, incorporating existing fans and more corporate and day visitor fans is a mix that can affect the atmosphere.
If Spurs do build a new stadium, my one bit of advice to the club would be to ensure that the people who populate the sections WHL that generate the signing, are given first refusal to sit together in the new stadium.