Frankly, it's a crapshoot.
The M96 engine has it's problems and a number of them do blow up.
But, the majority don't suffer an engine replacement.
It's just that you always have that sword of Damocles looming over you.
I owned an E-Type for about 12 yrs. and while I agree they had issues, they tended to be mostly nuisance ones while I believe the Boxster, in addition to a number of nuisance issues (AOS, RMS, Spark Plug Tubes, Ignition Switch, Top micr-switches, etc.) does have some more severe possibilities - D-chunk failures, IMS failures, etc.
If you get a good one, well maintained w/ service records, it's a nice car to own.