Expensive Tube Amplifiers

Regarding Quicksilver, guilty as charged.  Excellent amps at reasonable prices.  As for "vintage" amps, I assumed the OP meant amps from the 1950's-60's.  I would argue that buying a "classic" amp made in the 80's or 90's could be just a problematic as a Marantz or Fisher.  You can run into obsolete components or scarcity of proper schematics.

Larry, I consider Mundorf and Hovland caps to be birds of a feather, in the sense they’re both modern high quality film caps. I certainly don’t think all modern caps sound the same, and it doesn’t surprise me that either one is preferred over the other by a specific listener.

My Dynaco/VTA amps have been modified a few times, but they still won’t sound like a modern CAT amp or other top end tube amp that has better iron, better caps, better circuitry, better power supply, better wire, better chassis, and better tubes....at some point everything matters, and the better amps leave fewer stones unturned. 

Once you’ve been exposed to a true SOTA amp on a complementary SOTA system you’ll likely change your mind about how most vintage good stuff stacks up.  There are definitely diminishing returns per dollar spent, but the performance forges ahead regardless.

Yes both are film, but the Mundorf has a particular sound that is quite different from the Hovland or other vintage coupling caps that one might consider such as chocolate drops.  However designed, I consider the Hovlands vintage, not modern, because they are long out of production and one cannot just order them from a parts supplier.  For speaker crossovers there are a number of old capacitors that sound really good in some speaker designs that are, technically speaking, defective (e.g., caps with very high measured DC leakage voltage, but they work fine in crossovers because DC leakage does not matter). I am not saying vintage parts are better than new, I am saying that the opposite is not universally true and that there are some really good old parts that are hard to beat in some applications.