When it comes to lenses I've always felt that there's no point in buying Nikon or indeed Canon and then buying third party lenses. Sure they might be more expensive but there's a reason for that.
Third party lenses have their place. For people who cannot afford Nikkor, or Canon EL, or Minolta G, or Sony/Zeiss glass. The likes of Sigma, Tamron and Tokina make some very good lenses for a fraction of the cost, sure they've also made some lemons, but a little internet research goes a long way to avoiding them.
The average Joe looking at 4x6 snapshots of their family vacation would be hard pressed to tell you if whether they were taken with a $400 lens, or a $3,000 lens.
Personally I've got probably ~ $8-9K, invested in lenses right now. Most are high end Minolta G and Sony/Carl Zeiss glass, but I've got some cheaper stuff too, and right now I'm seriously considering picking up the new Tamron 150-600mm.. Why? Because it's $1k, vs $3k for the closest thing that Sony/Zeiss make, and it's a step up from the Sigma 400mm 5.6 prime I'm using now. Is the Sony better then the Tamron? Yup, by maybe 5%. But to the average viewer in 90% of the prints I'll do, they'll never notice that little difference.
The thing about optics is you pay a premium to get that last little bit. It's basically a exponential curve with X axis being quality and Y being price. Like I said the premium lens might be 5-10% better optically, but it's gonna cost 300% more.
The other thing that's driving up the cost of premium lenses in the digital age is sensor advancements. Used to be 5-10 years ago that a perfect lens wasn't that critical, because even a mid-range lens could out resolve the sensor. But now if you wanna squeeze every last bit of resolution out of the latest 24, and 36, and now even 50 megapixel sensors, you some super duper premium optics to resolve that fine.
I always had Nikon SLRs but never digital. My last camera is a film camera. I may be be able to get a digital Nikon this year. The problem I have is that my Nikkor lenses are older and are not fully compatible with the less expensive Nikon bodies. So I either get rid of the lenses or buy a more expensive Nikon!
On the other hand it's all a bit academic I can't afford to buy one at the moment. 
I'd hold on to those old Nikkors. Is the lack of an AF motor the only compatibility issue? Even on a body without an AF motor you can still use them in manual focus, can't you? Or pick up a used Nikon FF body from a few years ago, like a D700. One advantage (for buyers) of the rapidly changing digital market is the drop in resale value of a model, as soon as it's replacement comes out.
