I'm sure you have many more than 20 active years of sewing left cuz if we're supposed to quit at age 68, there's a whole slew of us in deep, deep trouble here!
Your last question - "How realistic is it to expect to even use the same machine for 10 to 15 years and be okay with not trading it in for something else?" - is the key question.
My Bernina is 13, my Viking is 25, my truck is 18, all my kitchen appliances are 27, my washer is 28, and my dryer is 42. All are mechanically sound (the truck, alas, has terminal rust) and perform their assigned functions with joy and vigor whenever called upon. The thing is, all but the Bernina and the truck have nothing whatsoever to do with computers or even electronics and therein lies your answer.
The Bernina software is no longer supported so I cannot add to or modify any of the embroidery stitches. I strongly suspect it will be that type of thing that drives you to upgrade at least once between now and 'forever' even if you don't crave any type of newly offered features.