i dont put on the kind of miles that ido does, but in over 20 yrs of Subaru ownership, yeah.. a lot of the aftermarket stuff is junk - especially axles and alternators.
i had a forester strut lifted 95 Legacy, and absolutely loved it! ran stock axles and had no problems. make sure the boots dont crack, and if they do, replace them asap - clean and regrease at the same time.. stock axles will go for a very long time. I used new KYB struts & tophats, and OE springs.. awesome combo for most drivers.
for alternator - best option, if you cant find an affordable new OE - is to get a used one and find a shop that specializes in rebuilding alternators & starters.. have that shop rebuild the OE alt. it will be far superior to any aftermarket replacement unit.
had the alt on my 95 go out.. put in a cheap aftermarket as a temp solution and had the OE rebuilt locally - cost me $140 - a bit more than an aftermarket unit, but worth every penny.. when i got it back it went back in the car, and the aftermarket one went back in its box and up on a shelf.. it sits there to this day.
in a previous car i had an aftermarket alt crap out after only 8 months, got a replacement under warranty, and that one lasted just less than a year. the one I had rebuilt locally was still going strong over 3 yrs later when i sold the car - probably outlived the car. almost wish i had thrown that cheap aftermarket one in before selling.. oh well
For a Subaru, OEM suppliers are the best option for most parts. even used is still usually better than any aftermarket will be. When those are not a viable option, knowing what is a good alternative will save you money in the long run.