Depending on one's point of view, the 918 either is a GREAT bargain or highly overpriced.
Porsche developed the 918 before the LaFerrari and the P1, independently. They had a internal target that they want to hit, that's their goal post. Then the Ferrari and McLaren came along and by that time the development of the 918 was well underway, and they either had the performance headroom to gain ground on the other 2 or the other 2 wasn't aiming high enough for their supercar to end up where they will be performance wise.
Taking into account the technology hurdle Porsche had to jump over in order to develop the 918, the price is actually a bargain. But for people who prefer a traditional internal combustion engine supercar without the high tech stuff, the 918 is a bit over priced with reference to the Carrera GT.
From Porsche's point of view, they gain nothing developing another IC engine super car, all the technology are readily available already. The 918 project is a challenge for the engineering team, like the old 959 project, building something unknown. Back then it was the twin turbo and awd system, now it's the hybrid technology. In a way it's is completely different than the Carrera GT project too, as the CGT doesn't have any ground breaking technology, Porsche just used everything they already knew to build it.
Traditionally, Ferrari's supercar kept their value and fetch more than anyone else's, so the expected value of the 918 will not be in the same ballpark as the LaFerrari, but then again Ferrari priced in the initial appreciation already for the LaFerrari, so not sure how much higher can it go. McLaren has only one, F1, as their track record, so the value of P1 is still to be decided, will it appreciate like the F1, not likely, will it appreciate? I think so. But no idea by how much.
Like Ferrari, McLaren priced in the appreciation factor too, and the 2 of them build a car with a much lower cost than the 918. So both of them will make a healthy profit selling those.
Porsche is in a different boat all together, traditionally their supercar do not appreciate much, the 918 won't be any different. I knew that from the beginning and I still buy one simply because I want to reward Porsche with my money for taking the risk and dumping so much technology into a road car. There is simply no equal among the marketplace right now, no other car can even come close to the 918 technology wise.
Porsche has and will learn a lot from this project, which means they will make better cars in the future, I guess in a way I am investing in my future cars with the 918 purchase.