I have been considering a folding bike too as our office is moving.
I have ridden a Brompton for 3 days in a row (borrowed it) doing what you did - car part way then ride in.
My thoughts? I thought it was heavy, very old fashioned in its construction, crap brakes, poor handling (very difficult to stand up and pedal when you get a steep bit). I tried the 6 speed one and the gears made no sense at all, 2 different shifting methods, derailleur and hub gear.....
The one big advantage is that it folds up the smallest of any folder, and you can get really neat luggage that fits to it.
But the price? Wowsers, its just daft!
On the other hand I've been looking into Dahon bikes. I thought about the Eco model which is only £350. 6 speed rear mech gears, proper 20 inch wheels so roll better over bumps. I didn't think they'd be great quality but I've just seen one in a shop and they look great. Alloy frame, stem etc. Much better looking than the Brompton too. Nice flat bars and proper grips, locking mechanism seems very secure and oversized. Proper V-brakes. The only weak point was the cheapy rear hub but I reckon I could spend £50 getting a new rear road hub and fitting it to make it more reliable and it'd still be a bargain.
It doesn't fold up quite as small but plenty small enough for a car boot.
I honestly don't know how Brompton get away with it. How can a bike which costs that much have crappy caliper brakes? Why do they have their own weird wheel size? I'd love to support a UK company but I just don't think they are worth the money.
I've also looked at Kansi bikes as they seem to be able to handle some kerb hopping and more "spirited" riding but they aren't cheap and look like a Dahon frame - no dealers round me so hard to see one in the metal.