Bought a 21j Yachty back in 2007....I wear it every day to the gym...it's in great shape and has been +/- 2 sec per day since I bought it.....it surpassed my wildest dreams for holding up...
My advise is to diversify your collection. Don't spend $500-600 on your first rep. Buy a couple of $200 reps first, see what you like. Sell some, buy some more. Get a nice rotation going. I have been collecting reps since 08 and never had problems with them. I do have about 16 gen/rep in my collection currently.
Depends on your luck. The only issue I've head is on a Breatling which I've had for a year, where the chronometer minute hand no longer works although the normal time function is fine. I'd guess a service could fix that easily, but to be honest, it really doesn't fuss me - who uses the chronometer function regularly anyway? A few other reps have had zero problems over the last year and a bit. Really is luck of the draw.
i have pam90 rep that has been running strong for over 5 years. the warranty on my gen carerra however, has come in handy three times in the two years that i have owned it. impossible to tell really.
I have over 20 reps with various movements - Asian ETA, 7750, and 6497. Been collecting since 2007. All have been running fine although most live in the watch box or winder as I rotate these with my gens as well. I've had only one problem so far - a tag carrerra caliber 16 chronograph with an Asian 7750 movement that started running slow since last year by about a minute a day. Totally unacceptable. I'm still on the fence whether to have it serviced or just live with it.