When trading an altcoin against BTC or ETH, remember that looking at charts’ face-values is not going to depict the entire picture, unless you apply certain normalization. The problem is that both parties involved are highly speculative. Unlike fiat currencies, which express high volatility under extreme circumstances (say, a war, or a financial crisis), their crypto siblings move double digits in a single day. This is caused by the fact that the cryptocurrency market is, for the most part, still a zero-sum game. Although fresh money is constantly being poured into it, trading opportunities are still limited to swapping altcoins with a small set of options (mainly, BTC, or ETH). Therefore, trading an altcoin against BTC or ETH, can't really tell you if a move has been caused by the lack/spike of interest in one of them, or the opposite motivation in the other. In simpler terms, if one cryptocurrency is seemingly losing value against BTC or ETH, it doesn't necessarily mean that there is a lack of interest in it. It might as well have been caused by a sudden spike of interest in BTC or ETH.
What I would usually do, is to grab certain price movements and essentially normalize them using the percentage of the base currency during the same time interval. Essentially, I'd try to mitigate a large altcoin dip or a spike, by dividing the percentage change of the base currency. This is essentially similar to trying to convert an altcoin against a fiat currency, or a tethered alternative. Another trick I'd apply is to multiply the altcoin's change by the percentage change in volume, and divide by the percentage change in volume of the base currency. To be extra safe, you could multiply the whole, by the daily percentage change of the total cryptocurrency market capitalization. I'd suggest that everyone interested takes a look at the CryptoCompare and CoinMarketCap'sAPIs. They offer an easy access to all of this information.
All of these measures should help correct large price dips and spikes, and would help attribute part of the price change to a movement of the base currency. What you should be concerned about, are systematic altcoin price changes, where the base currency is relatively stable (and/or the entire cryptocurrency market) is relative stable.
I hope that this tip can help you make better decisions. Remember that this is not trading advice, and you should always consult your own research before taking a proper decision!