Driving like a grandmother actually DOESNT help you.
Every engine has a BFSC = Brake Specific fuel consumption. In laymans terms...the optimum RPM and throttle position where the fuel is consumed in most efficient way. Usually its 80% throttle around the peak torque RPM. Yea you read that right....heavy throttle at between 2.5 to 4K is what my Civic likes, as do most cars. Think of it this way....with you babying the throttle you're keeping the throttle plate closed creating a large vacuum pump out of your engine. The power stroke is working against the intake stroke. The cylinder is going down but the vacuum created by it is pulling the cylinder back up. Not an efficient system. Thats why everyone is switching to Direct Injection, also why Diesels are so damn efficient. No throttle plate to create a vacuum and rob the engine of power.
Anywho, back to your examples...In most cases i accelerate fairly hard, get up to speed if not faster and throw the car in neutral....coast for as long as possible and slow as possible without pissing other people off. You want to get to the top gear as fast as possible and stay there.
The absolute most you will gain while hyper milling in the city is by driving as if you have no brakes....for instance....500m up ahead the light is red, you know that the red light wont be on much longer...if you maintain your speed you will hit the back of the waiting pack of cars and have to stop and accelerate again. Break NOW to a slower speed and coast the rest...with enough practice you will learn to time it so you will maintain speed and catch up to the back of the pack as they reach cruise velocity. Voila, you maintained momentum and used only a small amount of extra fuel to return to cruise speed.
I would seriously invest in an MPG meter. I have UltraGuage and its great.
http://www.ultra-gauge.com/ultragauge/index.htm Hooks up to your OBD2 port and depending on the car you can have 20+ parameters to choose from. Instantenous MPG, Trip MPG, Distance to Empty, Fuel level, Coolant temp, Gallons per hour, Oil temp, O2 sensor trim, intake temp, oil temp, TPS position, you name it. It also doubles as CEL code reader and can clear codes as well.
One thing that the Ultraguage showed me is just how much fuel the engine burns to maintaing its RPM. Heres my Civics example. On a hot day my gallons per hour while idling and engine hot will be in the 0.15 g/h area. Thats to maintain a 800rpm idle. To maintain a 3000 RPM in neutral, so nothing but spinning the engine and input shaft of the tranny it takes 1 gallon an hour burn rate!!! to triple the engine speed takes more than 6 times the fuel! Where does this information become useful? You know those long hills where if you stay in gear you almost let go of the gas to maintain the speed? Steep enough hill and you actually start to engine brake...well, That little gas pedal holding you're doing is sending fuel to maintain the RPM, nothing more as the cars momentum is propelling it down the hill. Throw it in neutral and watch that MPG go from 40's to 300's!! Long enough hill and you can turn off the engine. My SIR has electric power assist so i dont loose power steering and the vacuum booster has enough vacuum in reserve for a few brake times.
Damn, i wrote another novel.....