IMHO the rarer/high priced items will generally hold their value or increase due to the collecting aspect of the NS scene.
It can be seen today that records that are hard to get seem to make better and better prices whilst common records are hard to sell unless they become what is termed "in-demand" and that status normally only lasts a few months.
Additionally I feel that the supply of records has been really good for the last 5 - 10 years due to prices becoming known worldwide because of the internet and price guides, this has caused dealers in the US to search their stock for records that they would have overlooked previously and put them up for sale.
I don't think this good supply will continue much longer, couple of years maybe? If you look on ebay US now (R&B, 45rpm, highest price first) there are some good records for about 2 or 3 pages, then after that it sort of tails off rapidly. Also the condition of records is getting much poorer as the barrel is scraped.
Anyway records are for enjoying or for selling to buy more records, if you treat them as a commodity they must be one of the most volatile markets in the world.