Down to my last dollars. Any value in guaranteed minutes after they accepted the start?

yes

in fact, if you run fatigue settings on the depth chart, you should always promise at least 15m along with a start. the reason minutes has value of its own is because in the olden days, fatigue settings did not exist - you set the minutes of each players using the minutes settings. so, people could promise a start, and then put that player in the starting lineup on the 4-8 minutes setting. if you run exclusively fatigue, there is no reason not to promise at least 15m as well, often 20m depending on the sta of the player and the off/def ran.

Yah. Its pretty much unconscious for me - if I'm promising a start part of the action is to look at the stamina and decide how many minutes go with it,

If i can tell the guy will be a capable backup I always promise at least 10 minutes, sometimes 15. If I promise a start, and actually want him to start, I always promise 20mpg. Only times I don't is if I'm using the minutes setting and I promise a start but don't really want the guy playing much his first year.