Im sure it'll be reasonably successful in the first year. The main problem is that people are unlikely to visit it more than once. For a council investment I'd expect more sustainable projects.
An indoor arena with leisure facilities serves the locals with improved facilities AND attracts...
Load of crap. Can you seriously imagine people saying "let's go to Brighton, they have a cracking OBSERVATION TOWER". Can't see it enhancing tourism enough to payback the cost of it. As for the residents, some will go once and never again- meanwhile we're crying out for decent leisure facilities...