I think you will be better off collecting the fully manual ones as these tend to last much longer. the most you should get is the type with built in metering.
Those with too much electronics might fail in the future and become very expensive paperweights. The manual ones on the other hand, like the F2,F3 and FM2 etc, if kept properly could last a lift time. Also try to stay away from manuals with electronic shutters. Just another 2 cents worth of thought
I used to collect Nikon F and F2's, and these are only interesting to collect if you have them in MINT condition at least (better with box etc)....also, there were special models that are now rare, these are collectable. But sadly to say, those that you have exept for the F2 maybe are not collectable.....good thing is that these can be sold at the same price as you bought them (unless the SGD depreciates alot in the future). The F601 modified is interesting, but there not many people wanting these modified cameras.
Also, many collectors these days don't buy much anymore....any of them are getting old and senile,...and will die soon, so there won't be many people collecting for the moment. BUT there maybe comes a time when the current middle age people become intersted in collecting MECHANICAL cameras, so for them I am keeping some of my Fs and F2's
HS (an old birdie of 93 years!, going off the earth soon.....)
If you know how to buy and how to sell, you can make money by collecting cameras, but you have to know the market.
If thats what you want,.....the profits can be >10-25%, so higher than from gold or stocks which are more risky in my opinion. The gold price is now almost at its peak, so buying now is way tooo late...... stocks: can make but also can loose, and you don't know the companies that good, also there is alot of emotion affecting the stock market, so prices are not reflecting the real value....
I bought many things off eBay, when I started I could buy good stuff mostly from the US, and sold them off again to the US through eBay for profits of at least 20%, many times they went to more than 100% profit , but its an auction, so I have no control over it.....
There is a search function on eBay: you can do a search for items that were sold, and here you can judge how much they are worth, making to decide to buy or not easier, as you know what you can sell it for later....
Then use non-AI lenses lor! People have used them for years without problems, why must everyone now suddenly give them a miss? If you don't need AF, they are good enough....you have to know what you need first.
If you want value for collection, go for the brand. Unless its limited collection, it unlikely that old Nikon camera will retain its value, less to say going up. Collectables like Contax or Leicas (especially Contax sinces it possible it will be gone in the future) will have a price.