NCA,
From what I see those plugs look in excellent condition. I have read on the forums of people who have nearly 200K mi. on the original Iridium plugs. I changed the plugs (original) in my DIL's '99 RX at 97K mi. and I still have the plugs. They guage exactly what they called for when new. You're not supposed to gap iridium plugs and these were definitely original, had never been out. There was a very small amount of carbon on them but absolutely NO WEAR at all! The electrode is Iridium and the little "button" on the ground strap is platinum. Iridium is the hardest METAL known to man. That's why they don't wear. I absolutely agree with those that said stay away from Bosch (or as it is properly pronounced, Botched). With all due respect, I don't think your mechanic knows any where near what he thinks he does.
And no, you don't need an intake gasket. That was if you removed the intake manifold to change the rear plugs. I see no reason whatever to do that. I did have the throttle body off on my DIL's when I changed the plugs and the rears are still not EASY to get to, but definitely doable! I wouldn't think of removing the intake to change the plugs. Once I broke them loose I used a 1/4 in. ratchet with an adapter to back them out.