I supose it depends on how much you want to spend and how much you can appreciate the diferences.
I run quite a lot and own a few running shoes, but mostly I have two pairs (the rest are genreally "old shoes" that I keep for some reason or other). Personally I "need" one pair of shoes for running in the street and another one for trail running. I am used to running in the hills and mountains and I need a shoe that does not have me feeling every rock or slipping in the mud. Sadly, this shoes are a bit more rigid, so if I use them for street running they feel pretty wrong (I feel like I am having a fight with the floor ).
While street running I do speedwork as well as long runs. For me light running shoes work just the same wether I am running 5k, 10k or a half marathon.
5k: 20:12 (December 31st 2012)
10k : 42:30 (March 9th 2014)
Half Marathon: 1:35:27 (February 3rd 2013)
After completing my 10th HM it's marathon time. To be totally honest now it's recovery time due to an ankle injury, THEN I'll think about the Marathon.
Just wanted to vouch for the Newtons... I was skeptical at first, particularly because of the price, but I tried them and liked them. I got 568 miles out of my first pair and am at the 450 mile mark on my second.
As you probably already know, everybody has a different footfall, stride, and gate, not to mention pronation and all the other technical terms, so what works for me does not necessarily translate into somthing that will work for anyone else. But I found that the nubs on the bottom of the shoe encouraged me to run more "mid-foot", which in turn gave me a tad bit more speed without increasing the amount of effort. There are various dynamics involved and it took me many miles to get used to how to run in them. In the end I find that for long distances I will run more "flat-foot" vs "mid-foot", but when looking for a bit of speed, as soon as I let myself go "mid-foot" I have a nice boost of speed. Unfortunately I'm old enough that I can't keep the speed up for extended miles, but it does work.
The bottom line is, try the Newtons, but give yourself some time to learn how they feel and how to run in them.