I know this has been discussed in bits and pieces previously on this board, but I'd like to see a bunch of thoughts gathered in one place. I have a N/A 2002 V 70, bought new, now with just under 9000 miles on it. The owner's manual says to change the oil every 7500 miles. I've changed it twice so far, once about 3700 miles and once at the 7500 service; my idea so far has been to change the oil halfway between the recommended intervals to be on the safe side. But I've seen that a number of people here rely on the old 3000 mile interval, which is slightly more frequent than what I've done, and a number of you have switched to synthetic oil. But I've also heard the guys at Car Talk and some other people say that the 3000 mile interval used to be for real, but now it's not necessary, and it's just basically a way for dealers and mechanics to make extra money. I don't want to waste time and throw money away, but I *really* don't want to damage my car and have big expenses down the road just so I can save 30 bucks every now and then. So here are my questions:

1) Since I have a normally aspirated engine, is there any reason for me to use synthetic oil? Most of the advice to switch I've seen is from people with turbos, and refers to the higher temperatures those engines have to endure. Is there less stress on the oil in a non-turbo and therefore less of a need for synthetic? Is there a down-side to using synthetic? (I've seen references to leaks caused by switching.)

2) How does the 3700-mile oil change interval strike you for a N/A engine? Again, I think I remember the 3000-mile adherents being mostly turbo owners. Does 700 miles make a difference over time?

Thanks for the advice--and I'm sure others like me with little mechanical knowledge will appreciate it too.
--
Mark 2002 V70 8k