Coupla Points-
The 642 has a fighting trigger - if you are noticing creep and grittiness I have an instant cure - press it faster
You can make it into a match trigger, but why bother, plus it may, and a couple of you are headed down that path, influence reliability, probably badly.
Now, as to crud in the gun. The Smith assembly line is no doubt not what is was like back in the good old days, and I'd bet they still got plenty of complaints back then. Several have mentioned how dry the gun seems. It should be, relatively speaking. Most of us drastically over-lube. I wish I had said it first, but a close friend of mine puts it succinctly: "it doesnt have a dipstick"
Now, if we go OPEC with the lube, and proceed to stick the gun in the places 642s get stuck, pockets, ankle rigs, sock drawers and the like, what's goona happen? Every dust bunny out there will make a bee- , er ,bunny line for the innards, resulting in a graunchy trigger and guts full of goo.
IMHO, leave it alone. As long as it goes bang, the rest is up to you.
Mr. Trucker, please, for the sake of the gun, don't do it. You absolutely need the proper screwdriver and the method is a secret. Well somebody here will tell you but if S&W wanted you to play with its insides they would have put in a zipper, not screws. If you insist on DIY, get a Brownell's catalog and the appropriate Kuhnhausen book. If you are like me, you will keep a papre bag close at hand for the inevitable trip to a real gunsmith.