I echo the response of talking to Hayden. He has a wealth of information.
I can't comment much on the "oh boat series" (320, 350, 370, 380, etc) other than to say their layouts are more amenable to living on and lessons of the past were applied.
In 1991 IP switched from Polyester to Vinylester resin for the last few layers of fiberglass on the hull. This reduces the impacts of blistering. In addition, they changed the way they installed the chainplates and instead of mixing 316 SS with 304SS used all 316SS. There also was the lesson learned that 5200 does not stick well to Stainless Steel. I seem to remember that one of the recommended products was GE Silproof for bedding the top end of the chainplates where they exit to the deck.
I have owned a 31, 32 and now 37. Yes chainplates are a concern and for me, a mostly single-hand sailor, I chose to have Mack Yacht Services replace my chainplates as an insurance. From my experience, there is no way to tell if chainplates are compromised. I have a proctologist-like scope that I have used to look at them, but the results are inconclusive. I also have heard of some who chose to do the work themselves. I do not feel I am qualified to tear apart the cabinetry and do the job. Thus it is currently at Mack Yacht Services.
On the topic of tanks, on the newer boats there is less stainless and aluminum used for the tanks - that is a good thing. The big concern I have on the older boats is the potential of having to replace the water and/or fuel tanks under the floor. Under the teak and holly sole is a fiberglass pan that forms part of the structural integrity of the vessel and to get to the tanks you have to cut this, so my concern would be ensuring it is put back in a way that retains the structural integrity. I always filter water before it goes into the fresh water tank in the hopes of staving off the possibility of having to replace the water tank. Do not use any Chlorine product on these tanks. Twice a year, I T-off the hot water tank and insert a hose on the fresh water pump side, then flush the fresh water hoses with a mix of Chloronox, water and food coloring, then flush that with clean water. This way no Chlorine goes into any metal tanks.
My 37 (1997) came with the factory option of an in-mast furled main. I am a traditionalist and preferred the old sail config. I will say that I do like the furling sail and so far have not had problems with this system. A couple of important items to consider here: 1. the furling lift swivel (that raises and furls the main) needs to be in line - on my boat the halyard was pulling this off center and created friction and wear. MYachts took down my mast and serviced the system - while doing so, they re-routed the main halyard so it was in line. 2. the furling mechanism at the base of the mast (just above deck) cannot be serviced or replaced while the mast is on the boat. 3. the boom must be at less than 90 degrees for smooth unfurl/furl. Mine is set at about 85degrees and when furling/unfurling I loosen the boom vang and mainsheet to allow the boom space to rise.
I have sailed the 38 a number of times and it is a rock solid vessel. One thing I would consider is that with each new generation of IP the shape of the hull and keel were changed and improved. These 'underbody' improvements have an impact on up-wind and pointing ability. Additionally, on the "oh boats" the staysail system now includes the Hoyt boom. the value of this system is that the rise/fall of the boom is in a fixed position giving improved shape for the staysail on points of sail. Some of us have made some changes to improve the staysail control. I don't think there is any one 'perfect' solution. Hayden has posted an option he chose and I have posted an option I chose.
Also on the newer boats is the amount of teak. I like the traditional look, but it adds to maintenance. There is less of that on the newer boats and of note, the hand-rail is now stainless steel tubing.
Mac's two cents