I never sold my first bass. It was a 70's (made sometime between 1974 and 1976) Fender P that I bought used in 1980 for $300. I learned to play on that bass, played it in my first gig in high school, got in a band in college, modded it (Duncan Quarter Pounder and Bad Ass II, metal pickguard) in the early 80s, and then more or less quit playing in the mid 80s. It essentially sat in a case for almost 20 years. I started playing again a few years back, and then got in a band, using newer basses. On a whim, I took it in for a setup, and it played great after that. I returned it to its original look (tort. pickguard) and strung it with LaBella heavy gauge flats, and I love it. Although I now have other basses (a Spector and a couple of Js), I will never sell it.
If you really need the money, you should obviously sell it. But if you don't NEED to sell it, I would hold onto it.