Some random thoughts...

It doesn't matter what instrument(s) you play, if you don't enjoy being with the rest of the people in the band.

Specializing means learning more and more about less and less, until you risk knowing everything there is to know, about nothing at all. Learning a little about as many things as you can may tend towards knowing nothing about everything.

Having some knowledge of the other instruments can give you some insight into how they all fit together. Or at least how they should fit together.

I have a respect for bass players, based on their ability to anchor a band without getting all self-centred about it. Flashy lead guitarists are less than a dime a dozen. A solid bass player is someone worth knowing.

Drummers tend to be hard to work with, because of the personality types that drums attract. That and the moronic producers that insist on mixing tracks giving almost half of the total sound level to the drums. The best drummers play their kits as instruments that contribute to the overall sound. The real artists among drummers are rare treasures.

The 'best' guitar players, like any of the best musicians, place the good of the music ahead of gratifying their egos. I'd much rather jam with another rhythm player than spend my time backing up some needy, attention-starved, egocentric wanker. Such 'players' are everywhere, but that doesn't mean I gotta put up with 'em.

Learning to be useful at several positions is a good goal, I think. Ideally, it would allow you to explain how you want the other guys to play something you've written, and help you to understand what they expect from you.