The RMS/IMS leaks aren't super prevalent from what I've heard and that the problem is overblown.
The RMS and IMS should not be conflated in this way. Despite sounding similar and both technically being seal leaks, they're very different.
The RMS is "rear main seal". It's not unusual for it to leak some oil. This is fairly common (happened to our 997 C2S Cab), is known and acknowledged by Porsche (they fixed it under warranty in ours - we didn't even know it was happening, the dealer caught it and fixed it and told us when we picked up the car), and all it causes is some oil loss. As the flat 6 in the cars will burn oil anyway, you should be checking the oil regularly, so the only added concern is the stuff that drips out. It's also relatively easy to fix, so if your seal does have issues and you're digging around in there for something else, you can replace it, too. Not a big deal.
The IMS is "intermediate shaft", and the problem is actually with the seal for the bearing for the shaft. The seal breaks down and allows engine oil to enter the bearing. Engine oil isn't the appropriate lubricant, and can bring in contaminants, and can cause the bearing to fail. If the bearing fails, it'll almost certainly cause catastrophic engine failure. But this is rare - Porsche won't provide numbers and no one else has anywhere near a complete picture, but it's a small, small number of cars. The seal was redesigned multiple times through the run, and a 2007 or 2008 should be less likely to fail than a 2001, but neither is immune. The 2001 is easier to retrofit, if I'm remembering what I read correctly.
FWIW, the Cayman has also had engine failures related to oil starvation under high lateral load (cornering hard). There aren't good/effective fixes for this - there are some work-arounds, but they have flaws. It's something you're not likely (at all) to encounter on the street, but it's important to know about for the track. The 911 seems to handle lateral load better than the Cayman, though the basic versions are still vulnerable to oil starvation on slicks or aggressive r-comps on track. If you're considering tracking the cars, there are a lot more relevant details to know, but if not, it's insignificant.
IMO, you need to drive both cars. Some people love one and hate (or don't care about) the other. Some like them both. If you find you like them both, then it's time to dig through all these little details and weigh the pros and cons carefully.