All things being equal, fans would like to see more advanced technology on the ractrack. But the reality is that the more degrees of technical freedom in the rules, the more expensive it will be to compete, and the less close the racing will be.
NASCAR for instance is very restricted technically but is very, very successful because the racing is close. Formula 1 and Moto GP are two series with pretty open rules and they're always trying to rein them in to control costs and increase parity.
The number 1 thing fans want to see is a show. If you made Formula 1 totally unlimited you'd have gaps so big that there'd never be a question of who would win barring a crash. And it would be so expensive you'd end up with a single-digit grid of cars before long.