First, a definition. My definition:
Top of the Heap - this is actually defined as the top of the "slightly unreasonable" heap. For instance, if you buy a $7000 road bike, that's the top of the heap. Sure, you can drop $10k or even $20k on another more expensive road bike. But let's be real, if you drop $7k on a road bike everyone will know you're riding some serious bike and that it's pretty much the end of your rope with respect to buying a bike.
Given that, and the reasonable assumption that my road bike is about as Top of the Heap as I'm going to get, the answer would be, to buy a power meter. At this stage, I cannot imagine what else I would get for the road bike, save for carbon bars. But that's a drop in the bucket in this game really.
Then I guess you move on to things like coaching and so on. I'm not there, nor do I see myself going there, even though I did spend $$ on an actual training plan for cross season.
As for the casual rider, I'm not sure. Power meters, coaches, nor training plans aren't in your reality. So maybe an alternate bike, different brand but just as blingy.
FTR, I have 3 Niners because 2 were dropped in a fire sale. I got lucky with the SS admittedly. I woudln't have gone out and bought 3 of the same brand.