I have not changed my base hair/eyes in at least 5 years. But that isn't necessarily due to covering them up with wigs and eye items all the time.
I chose the eyes because they were smug and snarky looking. They are still my favorite eyes on Gaia, and I sport them regularly.
I chose the hair after a few changes because I wanted hair that would go with the maximum number of avatars. I used the 'wish' style for almost a year, but swapped it for ducktail because the wish has the 'swoop' front that doesn't layer well with hats and headbands. Short hair was easier to layer and use more items with so I never felt the need to change for longer hair, especially since more and more wigs were released. I cover my base hair more frequently than I cover my base eyes.
I chose the lightest skintone mostly because I thought it was a neutral color that went well with many colors. I stay plain old human because, again, options. I pretty much optimized my base for being able to wear the most choices since I change avatars frequently!