while i agree that you will find your share of northstar head gasket issues, it is fair to say that many, if not most, are the fault of cooling system maintenance and neglect. i believe there was a topic on this board regarding the most neglected systems in the car and this was most mentioned. my dad owns one 97k and has not had an issue. worked with someone with over 200k and never had this issue. seems to be the weak point of the motor, but if taken care of the motor does not seem to have this, or many other issues.
regards lincoln ls, you might as well mention issues with ball joints, transmissions, fuel pump systems that may require a new computer.... the 300m is tagged with the infamous-maybe its legendary-a606/42le transmission.
by the time its said and done, i would say this motor is no worse, and probably better than most, if taken care of. as far as adding coolant tabs-bfd. i suppose that whatever special chemicals go in such things as special honda trans fluid, coolant, etc. make them taboo as well? as a side, maybe gm could get some black ink if they just mixed the tabs right in with the coolant and called it northstar coolant-only available at the dealer-for $30 per gallon. plenty of other car manufacturers do this.
i completely agree that unless you buy new, from a service oriented dealer, be prepared for expensive issues. this goes for any car-not just the northstar. if the service records are there, i'd say its as fair a gamble as anything in its class.