If for example I bought Etheruem at $1000 and used it to purchase some ICO tokens, then Ethereum goes to $1300, does that mean I lost value?
You can use fiat currency as a comparison because it's not as volatile as cryptocurrencies are. If you buy Eth at 1000 and then buy tokens worth 1000 with that money, then in order to determine if you lost value or not, you need to see if the coin that you bought is worth more or less than your initial investment. If the tokens are worth more than 1000 then you've technically gained value. The ETH value doesn't matter unless you continue holding the coin. However, as with any investment, know that you haven't "made money" until you go back to the fiat currency you used initially.