Actually PSP dematerialized games cost 1000 to 1500 yens less on the Japanese PSN than in retail. But PSP games are hell a lot more expensive in Japan than in th west : 6000-7000 yens compared to 40€ in Europe. So the European 35€ dematerialized games (I don't know how much it is in America) are a real bargain!
If Vita games cost 10€/$ less it would be awesome but I rather expect something like 5€/$ difference and a reduced retail price to compete with 3DS. Difficult to say if it's really interesting though because it depends on how much memory you'll need to store games : the memory cards don't seem cheap...










