Because its an ill maintained POS that looks really good!!!!
Sorry to be so blunt, but thats the fact of the matter........ Qs NEVER rust...... Or at least its not too common....... My Q has lived in indiana for the last 60k for sure, maybe more, and there isnt a spot of rust on it (just a tad on some of the exhaust stuff, nothing really major).......
My car is low on power because of bad knock sensors, but its still got PLEANTY of get up and go to satisfy the butt meter....... It doesnt do a burn out, but it will still throw you in the back of your seat.......
I got lucky when finding mine....... The dealer I got it from drove it for 6 months, and they did a lot of things I would have had to do (fuel pump, new brake pads, tires, transmission fluid, etc).......
A knocked off hose in the back would probably be either a brake booster hose or the IAC......... Upper links, no biggie, 95 from Joe and a good DIY, about 25-30 mins......
The low power is defintely from the vacuum leak..... Ask him what it is, and then you could haggle for the dealer to get it fixed........
If you like the cosmetics of this car, and you really think its the one (with some help), than this is what I would do........ Say give me the car for 5500 (it will come out nicely to 5500 with indiana sales tax), and say that you will get all the FLUIDS changed and the vac leak done at their dealership....... I bet they'll bite it.......
Be patient, Qs are hard to find in good condition....... Because they are luxuary cars, they will look good, and seemingly run good, when in fact they are running by a thread......