A few thoughts (I was in Lisbon about 1 year ago today).
First, there are other things in Lisbon that you should not miss. I would include: ride a trolley up to the Castelo St. George overlooking the city, with a walk down the hill to the old city center through the Alfama neighborhood. Allow a couple hours. A walk through the old city center, the plaza at the foot of the old center, Rossi square, ride up the weird old Eiffel Elevator. Another hour or two. Belem district, with monastery, monument to the discoverers, and that crazy pastry joint - takes about 1/2 day, take a trolly there and back. That uses up most of a day, and that doesn't get you to any museums or include any down time for meals.
You say "We have only one day in Lisbon and of course, want to see it all" but in fact your itinerary actually doesn't include ANY of Lisbon! It's all "day trip FROM Lisbon" stuff and nothing in Lisbon itself.
Honestly, Sintra is not a half-day side trip. There are enough 5-star attractions there to fill the better part of a day, even if you're relentless: two palaces plus the Moorish castle, which requires some time and rambling. Also, I can't think of any good reason to drive to/from Sintra from Lisbon. The train is about as convenient as you could imagine.
We did not go to Cascais or Cape of Roca and Boca do Inferno, so I can't offer any opinions on those.
But I do agree with others, and think your plans are quite unrealistic. You need to either find a way to spend one more day there (which would still be a v-e-r-y full day) or cut out things.
Good luck, and I hope that helps.