1999 maxima traction control system light

I have a 1999 maxima (loaded) and last year I had two (one and then a
second different one a couple of weeks later) sensors (o2?) replaced
after running rough. Car ran fine then recently had 2 coils replaced
at a local garage after check engine light had come on. Now the
traction control system seems to be acting up - a couple of days ago
the light came on while driving and later went out - It came on again
yesterday but when i started it this morning it is off now. I called
a dealership this morning and they said they'd test it but sounds
like I probably need to replace the other 4 coils all together (and
perhaps they said plugs too but I wasnt sure whether that was
included or an additional option.)
A)Does this sound like the reason the traction control system light
came on?
B)Does this sound like the solution and is $578 a reasonable cost for
them to do a 4 coil replacement or is this unreasonable or a simple
type fixable thing??? Thanks, Dave