I hear ya...well I can't define proficient very acurately but let's just say that I'd like to be the regular bass player in a gigging band that plays out once or twice a month and doesn't sound like a$$. Great definition, eh?
Based on your definition, learning songs may be the way to go as far as your skills progressing to match your goal.
You can learn lots of songs w/o practicing sight reading, scales, modes or learning any theory. FTR, I'm not saying not to study those areas of music.
If you have a good ear and memory, learn/transcribe a few songs and be able to play along with the original tunes, you can be in a band sooner than you think. I suggest getting a "chart" notebook. One page per song with lyrics, cords, etc. Also get the song and keep it on file to match all the songs in your notebook.
Develop your vocals along the way and you'll be set, based on your goals as you described them.
The more songs you learn, the more proficient and accurate you'll be on the fretboard. IME, getting the physical agility to move around the fretboard accurately is one of the most important skills that will get you to your goal.
As far as being "good enough" to be in a band, remember, we all started somewhere. Maybe playing roots/fifths to start with but the more you spend time jamming with others, the more experience you get "being in a band" and realize what it takes to be on stage.
Also, remember that being in a band takes time every week, week after week, etc. Do you have the time and commitment? And, it's usually not a linear process.
Here are a few questions:
what are you doing now that you can give up to spend time being in a band? Remember, gigs take a lot more time than just the few hours that you play. There's travel, load in/out, getting home at 2-3am, sleeping in the next day. Then, if you play the next day, getting up and doing all over again.
Has your wife signed on for that? Taking care of the kids/family/home while you're away?
How about the ongoing investment/expense of auto repairs/fuel/equipment?
Then you have your own practice time to fit in along with rehearsals.
Here are few links to check out:
7. BEING IN A BAND
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First band
How "good" do you have to be?
Joining first band
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Joining a new band
Finding new band
Questions to ask before joining
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Auditioning
1 For new band
2
Getting back in the game
Red flag stories
Hilarious/Bizarre audition stories
"Never got to audition"
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Replacing a band member
Firing band member
1 Auditioning new member
2
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Leaving the band
Quitting
Giving notice
Getting fired
Quitting music?
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Reheasals
Wearing ear plugs
Band rehearsal/headphones
Learning band set list
Learning songs quickly
1 Rehearsal tips
2 efficiency
3 how often?
Check the link in my sig. below for more great TB info that may help you along the way.
Good luck.