I don't have a coach. I don't have a power meter. I don't have a GPS device. I don't run in Newtons, don't ride on Zipps, and don't own a swim skin.
I've considered purchasing all of those things. I've thought about spending money I didn't really have on things I don't really need, because they might (in most cases, will) make me faster. And in terms of improving speed, all of these tools are reasonable investments. I'm on the fence about Newtons (seems to me that they could go either way), but all the others, I firmly believe that they will make you faster.
But I'm not going to spend money on them.
Why? Because at this point in my training, they're not necessary. Sure, I could probably ride faster with a pair of Zipps. And I could probably get more speed out of myself with a GPS device, a power meter, a coach. But the truth is that I can still get so much out of myself just by swimming, biking, and running, that the improvements I would see with a monetary investment aren't necessary right now.
Hard work in the workouts is (right now) the most necessary thing for me.
Same goes for the workouts themselves. This year, I think I can drop 20-30 seconds off my mile pace in the 5k just by continuing the pattern of training I've been doing: long run, tempo run, intervals. There's still plenty of room for improvement for me with getting all my runs done, too. So I probably won't consider adding in additional workouts (hills, for example) on any regular basis until I see the current performance gains I'm making level off.
Chances are good that in a couple years I'll start to see my improvements plateau; my times won't get faster, my results won't improve. That's when I'll consider hiring a coach, purchasing new training tools, upgrading my equipment. And that's when I might start looking for new training methods, concentrating more on strength and plyometrics, re-evaluating my plan.
But for right now, consistency in working hard is my most necessary thing.