I think a stock KA24DE is pretty much indestructible with regular maintenance. On other s-chassis forums I've heard of many cases where the engine went well past 400,000 kms with little to none problems. Sounds like you're not really into the whole mod scene so I guess I'll just skip that.
Only peeve I sort of have is that (I guess for my s14 at least) I can't seem to get past 450~ km per 60L tank of gas with the stock ka24de.. no matter how hard or soft I drive.. =_+ and I use the recommend 91 so it costs me quite a bit being a student