I just reread this thread and will offer the results of some of my thoughts on this question. You may have seen my thread on tearing down the broken engine from my 2000 S.
What can I do with this 3.2l engine?
I have gone over several scenarios for this engine and did a list of necessary parts if I decided to rebuild it. Then decided to shelve it till I get my replacement engine installed in the car in the spring.
When you remove the heads you will see the condition of the bores, which, in my opinion, after much research, is a central question.
My price for parts once you split the case is a minimum of $1500 US. That includes a new but stock IMSB, reusing the pistons and rings, but new bearings and changing only the IMS chain guide. The new bearing carrier and head bolts alone are $700 US. Add a net $150 to this for ARP big end bolts.
One advantage of splitting the cases is that you get to inspect/change the IMS chain guide which you cannot see otherwise. But I have not seen reports of a lot of failures of that part.
Once I had disassembled the broken engine I started looking at the replacement engine and wondered if I should pull the heads and... but decided not to go there. I changed the tensioner chain pads, which were in very sad shape and am now putting it back together.
I tend towards thinking that the tensioner pads are more of a problem than the IMS bearing. I have seen 4 IMSBs (all double row) on engines with from 90K miles and up and all of them were still in good shape. I have inspected the tensioner pads on 3 of those engines and they were all well worn and on my replacement 3.2 engine (133K miles) they were getting close to failure.
So much for my very amateur 2 cents worth.