Market cap doesn't really mean anything. But if a coin is already launched and the MC is trash I would definitely do some research before throwing dough into it.
yes its better to do research by ourself rather than depend on marketcap because its only giving the presume for each coins. the best thing that we can do is we need to know their project especially the conditions of the coins in the market. but sometimes low marketcap can be important point if there are any good improvement from the dev and the team so the coins is increase the price and the position in the market so if we buy at the lower price, then we can make big profit later.