Need more info for a complete answer.
- Last time the Timing belt / water pump was replaced?
- Has the radiator ever been replaced?
If everything is running good I wouldn't worry about having to replace the Head Gaskets if they have already been replaced under recall. With as many miles as you have, it sounds like yours have already been replaced.
Provided everything is currently running good, the most important thing you can do is maintain a good cooling system. If you radiator has never been replaced I would look into replacing the complete cooling system - Water pump, T-stat, Radiator and Radiator Fan (These are known for getting brittle and Exploding - tearing up all kinds of stuff under the hood.)
I just replaced the HG on my 3.0 for its second time at 293k miles (First time was original owner estimated somewhere before 120k). Even at nearly 300K miles the bottom end was in great shape. I feel the reason I had to replace the HG was that the prior owner did not maintain the cooling system - I had to replace the radiator just to get the 4runner home when I purchased it - The radiator fan had exploded on him. I didn't get but around 3K on the truck before the HG went out.
If you do the work the head gaskets can be replaced for as little as $300 bucks - ~150 for the HG replacement set with New Head Bolts + ~150 to have the heads resurfaced, pressure checked and vacuum checked.
