The best I can give you is maybe. We all have our own favorite ways of doing things and our own preferences. What works for me might not suit you.
For me, NI seems to do OK. I use it to grab big keyword lists and to brainstorm ideas for new niches. Works pretty well for both. There are a few filtering options that'll help weed out some of the bullshit. You can also input your own KW list and get the numbers.
I don't know if it's any better than wordtracker or keyword discovery or any of the others but, I like it for the one-time cost. The support is good and they're always putting out updates. When the Overture tool went away they had an update and never skipped a beat.
I've tried the others and settled on NI for the above reason. I'm not a fan of recurring monthly charges. I have a crap load of these type things, some are OK some are pure shit. Fortunately, I either got them way cheap or free.
I believe, when it comes to keywords, there is no perfect solution. You have to throw a lot of shit at the wall and see what sticks. If you start out with a fairly large list and pay attention to what people are hitting on, then you can make adjustments.
Since I don't do much PPC, it doesn't cost me anything to put up thousands of pages on obscure words and phrases and wait to see what people land on.
I pay attention to the G - AW campaigns and the bid prices only for sites I'm using AS on, to judge if it'll be worthwhile to make a page and get any $s off the AS ads.
You might also consider keyword analyser, if you haven't already tried it. It gives you more specific info on PPC campaigns and does it for other networks, besides G.
KA tells you the G bid and click info for your keywords, too. It doesn't, however, tell you how many pages are indexed in the other SEs, where NI does. But, NI doesn't tell you PPC campaign info for Y or MSN.
It's a toss up, I suppose. If you're doing strictly PPC stuff, you might like KA better because it gives you more info related to PPC. Take a look at both and decide which will best suit your needs.
I see the price for NI has gone up to $127. It was less than a hundy when I bought it. They have a money back guarantee, though. My best advice is, if you're thinking about it, go ahead and buy it and try it out. If you don't like it, get a refund.