Cascais is not one market
Central Cascais, Monte Estoril, Birre, Quinta da Marinha, Carcavelos and the villages toward the Sintra-Cascais Natural Park solve different problems. Walkability, rail access, school runs, wind, plot size and proximity to Lisbon change quickly.
Further west, Malveira da Serra, Charneca and Biscaia are worth knowing about, particularly for buyers who want more nature, privacy and a village feel without being far from Cascais. You are closer to the Serra de Sintra and Guincho, with a very different atmosphere from central Cascais. The trade-off is convenience: a car matters much more, and traffic into Cascais or toward Lisbon can make a journey that looks short on a map considerably longer at the wrong time of day.
The premium can be worthwhile
You are paying for a soft landing: services, English-speaking networks, beaches, healthcare, schools and an easy relationship with Lisbon. For the right client, those are not cosmetic benefits; they are what makes the move sustainable.
The honest counterpoint is that the area can feel more international than immersive, and a larger budget does not automatically buy walkability. Decide which version of Cascais you want before comparing homes.