The California is a totally different car Nick and has established it's own market. It's already the "entry" level model and Ferrari are repositioning their line up so that the sports cars sit above the GT cars in price to reflect their higher performance - California below 458, FF below new 599. The California could challenge the 458 if Ferrari gave it a stiffer suspension set up and boosted the horse power. However, just as the Cayman could be built to equal or better the 911 Carrera, this will never happen as both companies have no intention of killing their Golden Goose. It would also take away the GT nature of the car. They were supposed to be introducing an HGTC package for the Cali to enhance it's handling but it looks like this has been shelved indefinately due to the success of the car in it's current configuration and the desire not to blur the lines between GT and sports models.

As to the 458 coupe there are plenty of buyers who would never buy a folding hard top variant as they will never use their car as a spider so why compromise, pay more and add weight in the process?