In a 10 team keeper, auction prices on high level players will probably get pretty inflated. Braun is pricey, but if he went for $44 last year then he'd probably go for even more this year. I'd keep him.
I think you should keep Kimbrel. Braun is a fantasy beast but you have him at value. Kimbrel would never go for $5 next year (I know he'd be over $20 in my auction) and since he's an elite closer, I value him over a starter like Beachy. There are just so many good starters and so few elite closers.
If you love Braun and want him back then you should be able to get him in the same price range. If someone else wants to spend $50 + on Braun in the auction then you should be happy. There are probably plenty of other players available at more premium positions that you could spend the money on if that happens.