16 years of the same system, time for change?

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Depends on what the OP has now, and whether the sound has been superseded by current offerings at or below a certain outlay of cash.

If the OP has top of the line gear that cost $20K plus, probably not.  However, cables get old and oxidization in the cables and at the connection points degrades the sound.  Simple maintenance with Deoxit may be all that's needed.
213runnin... there is merit to your comment. Prior to your comment I went and found some Squalin oil I bought a billion years ago (ok figure of speech) and wiped all connection down.
To say an improvement was not garnered would be a lie.At this point I now believe the cost to make a significant sonic improvement would be beyond my means. 

Good news indeed.  Decent quality gear will still sound good after 25 years or more, as long as it’s not abused.  You don’t sound like the abusive type.

There is one area that has experienced a revolution though, since 2004 or so.  Loudspeakers.  Better performance/SQ achieved at  lower prices.  Perhaps it’s the China Effect, as they’ve gotten much better at copying technology.

I bought some made in China KefQ750 recently and they so seriously trounce my old Paradigm Monitor 11v4, it is not funny.  The street price of the kef’s was about 1100.  That said, good quality speakers from 2005 will still sound excellent, it’s just that generally speaking, that level of SQ is cheaper to achieve these days.
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Doesn't hurt to listen to other stuff but If you still enjoy your gear and it stands up sound wise stay with it.
I changed after 10 years, but there are some things that last a very long time. That's the kind of thing I would change for. And in any case, it's just nice to buy something new, it gives you the strength to do something.