I may be in the minority, but I greatly prefer a simple set of rules to a complicated, highly subjective exhortation to price a companion based on the presumed impact that it will have on the narrative of the campaign.
Implicit in the pricing of everything in DFPRG, stunts powers etc., is that a strict price can be given to an option that expands the choices available to a player. Not every player in every game will get the same utility out of a a power or stunt, but the power does offer the same broadening of choices and so is priced the same independent of its "actual" value to the player and independent of what situations the particular campaign tends to involve. Thus nowhere in the DFRPG does it advocate offering a discount for strength powers in an RP-heavy campaign, or an increased charge for wings in games where hedge mazes play an important role in the plot.
I think that charging a player refresh to allow his companion to spend an equal amount of refresh is the way to go, and that trying to determine what powers might be "useful" to the character and which are just window dressing is not. There is always going to be a player who comes up with creative ways to use powers that the GM didn't expect, which make his companion underpriced. That leads to resentment at the table, which leads to conflict (the OOG, bad kind), and we don't want that.
If we do go that route, I still kind of like the tack I originally took: 1 stunt gets you a companion with no refresh but some skills, another stunt improves that with some amount of refresh, probably 2 or 3 (2 evens out the amount of refresh spent on the companion with the amount they have to spend, 3 effectively gives them a refund of 1), and further stunts increase their refresh by 1. I'm also intrigued by UmbraLux's idea to tie the refresh to the likeliehood that the companion is available to you, maybe also with a tie to how broadly they are willing to assist you. So a superpowered white court companion who cravenly refuses to risk his life might give you a better refund than a former Marine who swore a life debt and routinely risks his life for you without question. Though those differences (and the one Lux brought up) could also be well handled with compels . . .