Rappers or any of those cards with 50-75 Fans and 150-200 Skills. They're nice, but they're good when the time is right.
Well, I can basically narrow it down to two occasions:
You never know when you get that Epic/Legendary vehicle or when you'd go on a spree of getting 'people' cards that have more Fans than Skills, and if you are not prepared or distanced enough from Ego, you would inevitably fall into Ego (which you most definitely wanna avoid).
When that happens, the first go-to is Music Lessons, but again, if you have not invested enough in that department, you're gonna have a hard time grinding your way out of Ego.
The logical solution would be to eliminate the cause of Ego (list some cards with high Fans and no/fewer Skills, or put them into storage).
But if you're a hoarder like me, you might wanna go for buying cards that have much more Skills than Fans. That's when Rappers and pilots come into play. (I've noticed a pattern where they have more Skills than Fans)
They provide a decent temporary Skills boost and get you out of Ego without doing any Music Lessons. "Temporary", since no Skills gained in any way in Rising Star is permanent - they're to be burned with Ego. But if you haven't invested in Instruments, you're in for a lot of pain.
And only two of them are required for the mission "Rap Battle". The rest could be sold off in the market for STARBITs to help you open more packs maybe >.>
With the introduction of more Rappers and more print limits for each, getting your required Rapper for the 4th Zone has never been easier.
Also, it's not like you're gonna hit the 4th Zone in a week or two, and if you have enough juice to buy that many XP Boosters to help you get there so quick, buying 2 Rappers off the market wouldn't be so hard, y'know!
Secure your pair of Rappers and chill
And if you haven't done that, then no worries, you can get them for cheap.
And if you are getting too many and are feeling overwhelmed by them, then the market is your go-to.
Hope it was helpful!
Stay safe and Rap on!
Cheers~~