Is intonation THAT important?

[StringPicker6]

Is it bad that I don't really care about intonation? From what I understand, you play each string at the 12th fret and see if it's still in tune for the string note. But I don't play lead, and I don't play past the 12th fret. Any other reason to be concerned about intonation? It seems to be a thing for people who play electric lead.

[B0WIE]

Intonation is critical for me. Not as much for electrics (and definitely not for solos) but absolutely on acoustics because you hear so many notes played on top of each other. That's when intonation is relevant. Especially from the 0 to the 1st fret. The most overlooked area on an acoustic. The sour sound of a poorly intonated acoustic is really off putting for me.

That said, the guitar is not designed to be perfectly intonated and the SLIGHT flaws add a certain character. If you hear one of those guitars with the modified frets (the ones that look like roots), they lack a degree of fullness and power in chord delivery (to my ears) because everything aligns too tight. The imperfections in a normal fret board are something our ears accept.

But, I go way out of my way to make sure my guitars are intonated as good as you can get at the nut and saddle because it makes a huge difference in quality to my ears.

[William2]

Well, if you can't hear it and you're playing by yourself I suppose not. But if you are playing with a string player, they will let you know you are out of tune. My second Martin DSS-17 had this problem. The 12th fret was in tune with the 12th fret harmonic on the first 3 strings, but the 3 bass strings weren't. and it got worse from the 4th to the 6th string. The main theme on the Villa lobos Prelude #1 is played on the bass strings against a chordal accompaniment on the trebles. I had to bend the melody note on the string to make the note in tune. And I didn't have to go to the 12th fret to notice this problem. That's when I decided no more Martin guitars. But tuning is important to me. When I played lute, the lute had gut strings tied around its neck. You could make slight adjustments to the intonation of a note by lowering or angling the fret. I currently use the Johnny Smith method for tuning my guitar.

[Queequeg]

I use a lot of harmonics in my playing so intonation is important.
But as William says, if you aren't hearing it then I guess that's the main thing. 
However, I believe we should be listening for and attempting get the best sound the instrument and the musician are capable of producing. In other words, training our ears as discreet listening devices. We work a lifetime in the process; don't we?
It could be that your ear is acclimated to and thus accepting a certain degree of disharmony.
Even strumming a chord in the first position will set off high frequency harmonics which will enrich the overall musicality of the instrument when properly intonated.
Many 1970s vintage CF Martins were rather infamous for placing the bridge and saddle incorrectly making proper intonation virtually impossible.
Tangentially, unclrob has posted here more than once about switching a right-handed guitar to become a lefty without rerouting the bridge or repositioning the saddle and he insists that the intonation is near 'spot on'.
Go figure.