if you got the quad for 1200$ dont wory about it. burning oil wont hurt nothin, just keep toping off your oil and ride the piss outa it. no sense in rebuilding the top end because it burns a litle oil, its not exactly a high performance machine so who cares. but keep in mind it depends on how much its burning if its pooring out smoke like a 2 stroke diesel than thats too much but if it just smokes a litle than your fine, if it only smokes when you first start it up then thats just a valve seal - not a big deal
even if it was pooring out smoke, chances are i would leave it alone but thats becasue i would treat a 250ex like a total beater. if its a nice bike than you may want it runing top noch, its up to you. just dont think that you HAVE to rebuild it because it smokes.
i agree, but i'd carry an extra spark plug, becauce that oil will build up on the SP and cauce it to foul sooner than it normally would.