You've answered the question yourself! Those value resort rooms are TINY for 2 people never mind a family, I don't care how much time it might save, you will be on top of each other, ALL.THE.TIME!! There's no way that your kids won't keep you awake or wake you up, same goes for when anyone flushes one of the jet propelled toilets or goes in and out of their rooms. If your sleep is easily disturbed staying on site isn't worth ANY benefit you will gain. Since you've never been before you have the advantage of not having previous experiences to compare to and won't know what you *might* be missing. Truthfully, I don't think 30 minutes would be a huge advantage if you are relying on Disney transportation (most do when staying on site) because you're at the mercy of buses. I think you'd be happier staying off-site, realizing that the Bonnet Creek might as well be ONSITE, take a look at Google Earth and see where it is in comparison to some of the value resorts.
You will have a great trip but if you're tired from your kids bothering your sleep you won't enjoy it quite as much. Not ideal to come home from a holiday needing time off to recover!