Ask your GM!
Har har, funny joke. But seriously, what's going to come next are just guidelines. Even Crafts (basket weaving) +4 is going to result in a spotlight imbalance if you decide that every man, woman, child, or unknowable terror from space is susceptible to a lovingly-made basket of condolence cheeses. There'll be some more advice at the end, but take this all in mind that it can't stop you and your casual interest in one thing or another from tilting the game. It's just something to think about when you're designing the extras.
Fate on Balance
So the Fate Toolkit's got a "magic" section, which can also be a "sufficiently advanced technology" section, which might also be called a "sufficiently complicated subsystem" section. One of its components is how to think about balance when making your own. There are three components: group balance, or how the extra will be distributed among the group:
At its simplest, this means you must have a compelling answer to the question "Why wouldn’t I buy this power?"
balance in play, or how GM time will be devoted to dealing with the mechanics of the extra:
If the mechanics demand more of your attention—because they require more rolls, for example—then it's a good chance that power is sucking attention away from non-powered players. This can be addressed through thoughtful GMing, but better if it's not a problem in the first place.
and setting balance, or how GM time will be devoted to plotting around the extra:
Obviously, the more tightly you constrain the power, the less you need to worry about these things, but that runs the risk of the power feeling like an overlay on the setting rather than a true part of it.
But this is what you came for. Let's do this - though again, this is my call and my guideline for you. I'm not your players and I'm not you. I don't expect you to agree with my answers, just understand the principles of evaluation.
Paying Refresh for powers:
- Group balance: some people aren't going to want to pay Refresh for powers because they want to charge out the gate with a handful of Fate Points.
- Balance in play: not much mechanical work here! Some people get a bigger stack of points than others.
- Setting balance: but, yeah, you could definitely spend more time working out how to compel the short stacks into a reasonable fate point total and not as much about the people with no powers. That's part of why I favor the Robo approach - everybody has a fixed refresh and number of stunts, and anything that stacks over that gives the GM more Fate Points at the start of a session to mess with anybody they want.
- Group balance: a single free Invoke probably isn't going to appeal to some players as a stunt feature, given what else stunts are capable of.
- Balance in play: sometimes you wave around two Fate Points instead of one. No big.
- Setting balance: maybe this could create the opposite of the refresh problem? You'd be writing away from people with a Signature Aspect sometimes, because you don't want them to constantly fish for super-compels? I haven't found that this has been a big deal for any of the sessions I've run, though again: not you, not your players.
High Fantasy Magic:
- Group balance: players can take or leave this one, I think? Without spending refresh you're basically just devoting one of your Aspects to a particular set of Aspect Permissions. It's no big deal if everyone's a little bit magical, but that's really on the level of "variant character concept".
- Balance in play: if some people go deep into magic crafting or summoning extra dudes, this could get kind of tilted. Worth keeping an eye on any one person's total number of schticks.
- Setting balance: magicians can plot to make big magic effects. Definitely need to make it known to non-magical characters that they can plot to make big effects too, it'll just look different.
Words of Power:
- Group balance: permission aspect, must have Lore, needs some sunk Stunts for power. Not for everybody!
- Balance in play: dynamically stitching together spells and rolling to cast them can definitely eat some time, unless your mage GMed a Burning Wheel system and is great at adding up Ob.
- Setting balance: since you get all the words all at once, this is a pretty big risk for just rolling Lore instead of anything else. Also there are big corker spells that would need a lot of setup.
And, as promised, some ways for you to see if you really are keeping an even keel.
- Roses and Thorns/Stars and Wishes. I'm not your players, but you're not your players either. So at the end of every session, ask them to tell you something they enjoyed (rose/star) and something they'd like to see done or done better next game (thorn/wish). This is all for everyone's fun, right? So see how you're doing.
- Per-player Fate Points. Fate Points can be represented by literally anything, so see if you can get some literally anything in your players' signature colors. If you keep a separate "discard pool" from your source, you can see how many points players are getting and spending every game. A little imbalance in one session isn't bad - certain sessions will tend to lean toward certain characters, because of the variance in plot on offer. But a long-term trend may mean you're plotting too much around one character.
- Per-player time coding. You're really not going to pull this off unless you already record your sessions, perhaps for streaming or something, and it's a big stack of time even so. But if you're really concerned about spotlight balance, go over the actual session play and see where the spotlight's pointed.