"...tube pre's are essentially expensive capacitors surrounded by a bunch of other junk..."
Hmmm, depending on the definitions of expensive and junk, that description could technically apply to any audio gear, even including multi-driver speakers.
Upgrading amplifiera.
A number of audiophiles upgrade their amplifiers. Is this a futile quest for the holy grail or are those upgrades a smarter way to dramatically improving the sound then purchasing a new one.