I'm undecided whether I agree with your thesis, but I definitely disagree with much of your evidence.
RSS was primarily a nerd feature in the first place
Why is the concept of a bookmark that can tell you when it has updates a nerd feature? This was essentially Apple's implementation in Safari. (At least, initially, I haven't paid attention to how it evolved).
iTunes seems to have everything else in there already, one more tab that reads "RSS" wouldn't hurt.
This exists. It's called "Podcasts", and it's wildly successful.
Dashboard being a failure is clear.
Here, we agree. I think that if it displayed among your other windows, rather than being relegated to a modal view, it would have been much more successful. I believe this was a decision for performance reasons, but it was still never corrected once performance was no longer a concern.
Spotlight ... where was the value back when it needed to re-index on every reboot and dragged your computer to a halt?
Anecdote != data, but I never experienced these problems, and I was running 10.4 on a G4 iMac, which originally came with 10.2.
Honestly, I think Sherlock and Dashboard would be your two strongest arguments.
Then again, let's look at iTunes. Sure, it's bloated now, and sure, they bought it, but the reason it won is because it really was excellent. (I say this as someone who used Audion for years and I still have a giant place in my heart for it). Solving music library management was exactly the right problem, and iTunes (& SoundJam before it) got this right far before their competitors did.
How about iChat? It's built in, it's integrated, it's pretty darn good, but almost everyone I know who knows about Adium uses it instead.