i agree that buying quality is a good idea, it's daft if you're continually buying and selling on and then buying again (though i would add that buying expensive stuff, if all the forums I go to, is no defence against that- some people just buy and sell a lot, and others don't). But it depends on the situation, too. If you play a wide range of stuff, 4 "good" guitars (say a strat, tele, LP and LP special) would arguably make more sense than one "awesome" guitar costing the same as those four put together. Ditto with amps.
EDIT: ^ yeah, i agree. I don't agree with rationalising it at all. I don't drink or smoke, and I don't see drinkers or smokers rationalising that (or anyone else who buys anything, ever), so forgive me if I don't feel bad because I like buying and playing guitars and amps. At least it's something constructive. EDIT: cr@p, that's a rationalisation.