Steve, with all due deference to you, in absolute terms, you never stop upgrading if you can afford it until you have a gigantic listening room that's fully, acoustically treated and was built out for audio in mind and it has no noise pollution..
In the normal world, you are looking at how much speakers/subs your room can take, how much noise is in your listening environment and how much treatment can your room accommodate. Also, if your amps have a SNR below 120dB as well as broadband distortion less than 0.01%, there's a good chance you will hear no difference between competitive models. The only difference will be with amps that are more likely to change their behavior with highly reactive speakers (less load intolerance).
Having been around for a million years, here are my thoughts:
- You upgrade speakers after about 10-15 years. They'll still sound good, but will no longer be great for their price and could be somewhat worked out. Speakers keep getting better all the time.
- If you've bought really great electronics these days (Benchmark AHB-2 or such), you only replace it when it fails. Swapping out amps regularly is a fools errand.
- Also, when are talking about any DAC's, pre's, pre/pro's, that stuff is so good now that there is no improvement they can make that will be audible with an upgrade in most cases. Sorry, but it's true. If you have a $500 home theater receiver, sure. If you have really good separates, it's most likely a waste of time and money. drive them into the ground until something goes wrong... just like a car.
I remember going to a place in Jenkintown, PA that sold new and used equipment and had been running an ad for years in the back of Audio Magazine in the 70's, 80's and 90's. Very cool joint. I was there to check out the Carver Sub, but was amazed by the amount of used, high-end gear there. Some was not even old.
The salesman told me, "Some of these power amps (really great stuff) were bought here a year or two ago." These guys were chasing the upgrade dream where it's not about the sound, it's about the status of owning the equipment and how good that makes them feel.
Steve, I think you'd be hard pressed to find better passive speakers, at their price, than the ones you have. Personally, in my home theater, I'm using five LS50's and four, Rythmik servo subs. Hey My rig can produce more bass, more cleanly than yours. So what? You still have a great pair of speakers that probably has nicer treble. So what?
Do I want a better system than this? Sure! Do I need one to clearly hear the music in a treated room with Dirac running? Most likely not.
Unless you envy equipment more than the music it's playing or you bought a piece of crap to begin with, there is no reason to replace anything in your system until starts failing or you are doing a big upgrade. Do not become an audio equipment junkie.