Most Altcoins lose value over time, its just the matter of time.
Keep this in mind when holding Altcoins for medium and long term and choose wisely. Altcoin is not meant to be long term. If it is then its just a reason made up to enter a trade.
Projects or Coins now have a higher daily trading volume and a broader community to back them up in a continuous development.
Ethereum ETH, Monero XMR, FCT Factor, and DASH are the leading Coin with the highest daily volume. You should follow the chart and define which stage you are on and would it be a whale's consolidation phase. At the right time and a good press release on the project, the pump will begin and all you need it waiting for the money to pour in. Remember, the winner is the one has the most cash, not the most Bitcoin.
Im not sure why you think altcoins will depreciate i value over time because not all of them are pump and dump schemes. Sure there are many low volume altcoins that can easily be manipulated by a whale or a group of whales but the coins you mentioned above trade at very high volumes and are much harder to manipulate. I think they move with the entire crypto market and are not just controlled by a small group of individuals.