Correct, there are a few instances in which altcoins went up in value on their own without bitcoin doing so first but this is so rare that people cannot really count on that, so until bitcoin is on a bull run then the possibility of altcoins going parabolic are basically zero, and since this is not going to happen during this year or the next one the ones that are holding altcoins will have to wait for a long time before they see any return on their investment.
It is hard to say about values of altcoins. Most of them are created in bull run, during a hottest period of a new trend, and you can say a market price at $100 is its value, if a coin listed on big exchanges, and make a top at $100. It is not a real intrinsic value of that coin. It is just because of FOMO and overvalue it from investors or traders or speculators or gamblers.
After such top up, altcoins will fall back and even will be divided 10 times, 20 times or 100 times. At that time, you can start to consider saying about their values.