Slightly off-topic... All the routers I've owned (cheap or medium-priced) have held up a few years, then either started getting flaky or were just way slower than the new versions on the market so I upgraded. A few years is usually good enough for me, cause by then I'd wanted a faster upgrade anyway.
But I'd always wondered why these things all seemed to go flaky after around the same period of time - like something electronic was wearing out. Long story short, it's the wall wart power supplies that wear out - specifically the filter caps in the cheap SMPS (switch mode power supplies) they ship with everything these days. When the filter caps dry up from running continuously and too warm for too long, the wall wart stops putting out DC voltage and starts putting out something in-between DC and AC. Took me hooking up a scope to figure this out.
Anyway, if your router or modem is acting flaky, has a DC wall wart, and is still good enough for you that you want to keep it going, check for ripple in the DC the wall wart is putting out, or try subbing in a known-good wall wart to see if it fixes the problem.
Cordless phones suffer from this problem as well... They get super noisy when the wall wart (or internal filter caps if it runs on AC) starts dying.
Glad to hear your ISP let you keep yours
-Pete