RE: lvl 55+ gear
I have noticed that Quest gear from the 2 main quest lines have been pretty good, some ppl may not have to really stat much if all they want to do is play the quest lines.
Having said that, dirty statting is a good idea unless you are using nearly the best EQ for your class that you can get your hands on.
Obviously, if you have the BEST current helmet, then I would put the time & $$$ into statting it right.
If you have a helmet that's within... the last 10-15 levels, I would still stat it right, but not really focus on making the best choices. Instead, focus on the right stat "family". ie, if you are a melee type that gets 2x pa from str, try to stat str/x stats. This will get you on your way to getting better gear that you can be more discriminating.
If you have a piece that you know you'll keep for a while, for whatever reason, but don't have any deep attachment then I would look @ dirty statting. Sometimes just having 3 t5 stats on t3 gear will make the gear "good enough" to get by for a while, since you'll get an extra 20% bonus to pdef/mdef & whatever ghost stats there are.
The last thing is.. if you have a piece that you just picked up & don't think it's worth statting.. don't.
^-- all of this is relative