At the risk of being branded a heretic, I'd like to offer my perspective. I'm a mechanical engineer (early 30's) with a wife and 2 kids.
Have you driven the MS3?
I drove it in the same afternoon as a bunch of other cars, and it didn't really set me on fire. I was expecting perfection after reading all the fawning reviews in the buff books and internet. It is bumpy and loud, and the back seat is pretty short on knee room. The shifter is not great. I could not get a comfortable driving position. I'm 6' and skinny with long arms.
The turbo rush is OK, but you don't get full power until 3rd gear, and by then you're over the speed limit nearly everywhere. It is a fast car, but I'd rather have more torque down low. I couldn't take the front drive compromises. Maybe I got spoiled by my WRX. The MS3 was not what I was looking for in a daily driver.
I'm not trying to trash the car, but don't fall in love with something based on what everyone else thinks. It is a pretty good value, but it is not really "touched by the hand of God!"
Only you can answer the question of whether you'll be kicking yourself because you didn't buy the car you really wanted, or kicking yourself for buying the car that takes premium gas.
Some background:
Cars I've owned:
'85 Omni GLH Turbo (manual) --lots of turbo lag and torque steer. Lots of fun, too
'92 Mustang LX 5.0 (manual) --torque
'02 WRX sedan (manual) --no torque
'91 Volvo 940T wagon (auto) --not really fast even with the boost turned up to ~11 psi
'99 Accord 4 cyl sedan (manual) --took this from my wife after we bought the family truckster
Cars I drove last fall while shopping: Legacy GT, WRX, STi, E36 M3, E46 ZHP, MS3, MS6, G35, CTS-V, G8 GT, supercharged '01 Miata, E90 330i sport, E90 335i sport.
I bought a used 335i with the sport package. After I drove one, I could not bring myself to buy any of the other cars. However, some of the other BMWs I drove were a bit of a let down, even though they uniformly got stellar reviews.
-Brian
P.S. Sorry for writing a novel above!