DR,
Speedwork will make it easier to hit max, but that's not really the point, if your target is racing 5k upwards, as you won't be running those near max.
My last 10k was interesting, apart from it being a big PB, in that my legs and heart were hardly troubled but I couldn't get enough air in my lungs to satisfy my voracious aerobic appetite. I was running at 90%of max HR. Speedwork will help open up some of the deeper parts of my lungs and increase my top end speed, but my HR still won't be anywhere near max.
I could probably hit max over short sharp intervals where oxygen supply isn't the critical factor, but I know it will feel way harder than it used to.
It's an odd thing - I can run so much faster than I used to be able to do, but it requires so much more effort, due to the work needed to overload what is now a much more robust aerobic system!