When does one know it's time to upgrade?

@audiomaze That isnt me in the photo :p Just thought it was pretty fitting posture for an audio forum.
I sit in a low back silk and down filled upholstered chair. I actually find leather to be a little too reflective. I also prefer to have a chair with an internal structure made of wood for listening in.

As Samadhana so stated when you start listening to your system less and less more than likely its time to upgrade.  I personally start my up grade every 5 to 7 years with a better Preamp next speakers which I don`t think I`ll be upgrading my Maggie 3.6`s anytime soon I`ve own for 6 years in conclusion  my cartridge which in IMHO is the right route for me to improve a system

I have several music systems, living room, shower, garage, boat, car etc. I spend most of my time enjoying music and not upgrading.

Maybe, in the winter, I might get bored and get a new set of tubes for my amp, but now, it is time to go outside and enjoy the spring weather.

As someone who has been building systems for 20 plus years my experience is that while the components are absolutely extremely important, in terms of sound characteristics, nothing is going to make a difference more than a speaker. I've always auditioned multiple pairs of speakers at a number of different retail locations before buying a pair. Once I know what speakers I want I them start working through which electronics I want to push them. This is where it's important to have more than one retailer that has your speakers because you may want to try 2 or 3 sets of electronics at each place. Last part is source. It's extremely difficult to know what to expect from a source unless you have an idea of what the system is going to sound like and how revealing it's going to be. 

To me, it seems you have some quality components and, though somewhat satisfied, feel your speakers are the weak link. I think your probably right. Based on the other components you have I'd look in the 2-3 range and keep a really open mind. Go listen to a lot of speakers. 

" But what i can't wrap my head around is how anyone has any sense of direction when it comes to pairing equipment"...

There is, as someone mentioned, the approach of sticking to one brand-- finding a "house sound that you like", although I've never done that. 

Others take an engineering approach, basing decisions upon measurements. I haven't done that, either.   

I believe it's crucial to know what actually floats your boat and you apparently do, having said " I really enjoy being surprised and wowed by dynamics, sound-stage, separation and weight of the sound". 

This sort of knowledge should enable you to evaluate others' reviews of gear as well as evaluate gear on your own with some success. And yes, your sense of what pleases you may very well change over time. 

My path has been-- like many others, no doubt-- meandering. I made some mistakes early on that taught me valuable lessons. Chief among these was never buy anything I can't demo at home with a return policy. 

There's also been an element of good fortune, luck, kismet, grace, karma-- call it what you will. In my case, the Silverline monitors I still own were recommended to me more than 10 years ago by a fellow A'gon'er. I knew very little about audio, at that point. For some reason, I just felt compelled to take his advice and it turned out to be a very fortuitous choice. 

Around the same time, I met a local independent dealer who was willing to bring gear to my house to demo. 

I'm an artistic sort and trust my own aesthetic judgement most of all but I  also tend to obsessively research gear online when I want to upgrade. 

I've never had huge amounts of cash to spend on audio so have had to operate within fairly modest contraints. This has often led me to purchase gear from smaller, lesser-known manufacturers with low advertising budgets who cannot sell based upon brand-name recognition and offer high bang-for-the-buck. My Wells Majestic integrated is a great example.
I couldn't afford a new one but Jeff Wells sold me a demo unit at a price I couldn't refuse (with a refund option). I can't imagine ever needing to upgrade this component.

There've been times when I've started out believing I needed to upgrade a certain component but ended up upgrading something else entirely and have been very happy with the results. I'll close with an example...

I've never been completely satisfied with the bass response of my system. I have no room for subs and I figured I would simply have to accept the inherent limitations of monitor speakers in this regard. 

Very recently, I felt the upgrade itch but had less than 1K to spend. I thought I'd revisit vibration control and demo'd a Symposium Svelte Plus Platform with RollerBlock Junior+'s under my Moon transport.

The results floored me-- the degree of unexpected improvement in terms of bass has been amazing. I mention this as an example of another facet of this hobby-- you never really know how a given product might impact your system.

I have no idea whether any of this is relevant or helpful to you but seeing as most who've responded have addressed the upgrade timing aspect of your initial post, I thought I'd chime in regarding the other aspect.