I agree with most of what has been said above, although there's an element of rose-tinted glasses at play too.
I think the quality of candidates has been in steady decline since series two. Since then we have generally had 2-3 credible candidates each year, and then a series of increasingly extreme characters - the 'chancer' (Tre Azam, Michael Sophocles), the 'TV wannabe' (Kate Walsh, Katie Hopkins, Katie Wright - what is it with Kates?!?), the 'loud-mouth' (Stuart Baggs, Adam), the 'misogynist', the 'organiser' (Helen Milligan, Stella English) and so on.
We're now at the point where the task is frequently just half the episode, and it's all about the boardroom - which means we also get fewer pithy observations from Nick and Karren. Which means the idiots get their airtime over the quiet, competent ones.
I do feel the show is going downhill, although after 8 years that's inevitable. The tasks feel tired and repetitive, and in reality have nothing to do with how the competition is won - it's all about an idea, not how good a project leader you are.
My solution is quite dramatic. Instead of having weekly tasks which are basically all fly-by-night sales operations, you make the entire series one big task, and the teams have to project manage it from start to finish. So week one would be about coming up with the idea and researching the concept. Week two might be about product development. Then there would be a week where they have to pitch to potential buyers, then maybe test-sell their product in a market/shopping centre, create an ad campaign and finally launch it. Every week would test different skills, and teams couldn't just walk away from the task at the end of the episode and act like it never happened. And at the end of it you would have a genuine winner, potentially with a real business to run.
It's very different in concept to the current format and it's much more business-oriented, but could still be entertaining given the potential pitfalls at each stage. Be interested to know what people think. It's just an idea for fun, really - it'll never happen.