That sounds like a very good way to do it. We'd toyed with: allowing a re-roll, allowing an additional 1d10 added to the roll, or a +1 per point spent. There wasn't guidance as to if those point came back or if they were just spent (or how Power returns if at all) so we decided that a good night's rest was either reset back to your base score OR a 1d10 roll to see how much came back after sleep up to your maximum. There's lots of room in the game to tailor as needed. We had a lot of fun with it.