I'm not sure but I think those are good numbers for 158k. I believe they say it should be atleast 180. But some guy posted 120 -130 numbers and said he car still ran well.
I haven't had a chance to drive the car yet since I did the seafoam but it seemed like there was somewhat better response afterwards. The idle also went back to a more reasonable level (used to idle around 1000rpm). As for what it does, it makes a very nice smokeshow. It's supposed to clean out the carbon deposits from your combustion chambers, valves, stuff like that. Apparently the more smoke, the more junk was cleaned out from your motor.
FWIW, if you want to read a ton of info, this was quite in-vogue on SN a year or so ago. There are a zillion threads about it (I am not being a smarty pants - I dont know if you were aware that there are a lot of threads about it).
It is about 5 bucks/can at Autozone. You can add it to the fuel tank, crankcase (oil) or run it through a vac line. The latter-most method is the most popular.