I do older mustangs, but can answer a few questions for you and give you a little info.
Hondas hold their value, people seem to think they last forever, but I have seen my fair share with problems just like any other car. Not bashing, just think they are more on the level.
Mustangs are fun cars, I don't really like the look of the newer ones, but won't rag on you for it. Its much easier to make a mustang go fast than a honda. I saw a guy with an auto gt 98 drive the 1/4 mile for the first time (had never been on a track), with the air on, and a passenger and turn a 14.9. What you are mainly getting up front is torque. Hondas(and all the smaller cars)just dont have it. That is why they have to strip the interiors out of them. It really does make a big difference. It I did that to my car the results would be very small. I can also run with a passenger and it does not effect my times but like a .10 of a second or so.
the 4.6 motors are fairly new so long term standings on them are not really available. As far as the car falling apart on you, I think they are fairly well made. I don't see a lot of them completely falling apart. all cars have their problems, but I have not noticed too much. For example, on my 94 mx6 its well known that the power window switchs brake, the distributors have issues, and such. I don't know of much like that on the newer mustangs.
It makes little sense to me. I borrowed a friend of mines honda civic hatchback. I felt dirty driving it. It was a low end model, but it seemed like so much of the car was really made pretty cheap. I may be spoiled cause my mx6 is an LS with the leather wheel and shifter, but little things like pennys stuck in the dash to keep it from squeking and such seemed really bad.
I AM NOT BASHING IMPORTS OR HONDAS, just expressing my experiences. if you pick up a gt mustang 5 speed, you will be roasting imports left and right. Add some mods like exhaust, throttle body, etc you will be downright untouchable by anything but strip prepared cars. Hell, hook up a supercharger and its all over!