At the 8U level, I tend to agree with the USA Hockey ADM philosophy of enforcing equal minutes via a forced line change at a whistle or scoreboard buzzer every 90 - 120 seconds. That way, we, as coaches, don't have to think so much about who's had more (or less...) ice time - we just split our kids into roughly equal groups and change at every buzzer. The way I see it, there will be plenty of opportunities in the older age groups to shorten our benches while chasing victories - but 8U is NOT the time to start that.
As far as 'meaningful minutes' go, as trite as it sounds, we can't let ourselves forget that these are kids, NOT mini adults. Especially at 8U, kids' motivations are different than ours - thus minutes we might consider especially 'meaningful' as adults may not have any special significance to the average 8U player. Put differently, individual kids (generally) don't care if they're the ones relied on to be on the ice with 1:30 to go in a one goal game...they just want to be on the ice, have fun, score goals, and celebrate afterwards with their teammates, greasy pizza, and overpriced video games.
Don't worry about choppy teaching. Kids are generally episodic learners - meaning any overall theme you might be trying to establish will likely be lost on them anyway. Get the teaching you can done within the framework you have to operate and, above all, keep them smiling. If the kids you coach at 8U are excited to sign up for 10U, then you've done a great job!