I think the altcoin market is shooting itself in it's leg with all the new ICO's and coins with a small marketcap. The big amount of small coins make up for a high volatile market. Because of this 50% + spikes aren's something strange. I think this is what slows down the attraction of new serious investers and only attracts more gamblers and other people only interested in a quick buck without any care about what the projects are really about. Attracting players like this will make the market even more volatile and less trustworthy (vicious circle) like we see lately.

What should happen to make people regain their faith and attract serious investors to increase the marketcap in a sustainable way?

Some (probably impossible and maybe bad) ideas:
-Stop the exchange of a coin temporarily when a coin hits a given increase/decrease  in a predetermined time (say random 30% in 1 hour);
-Give a minimal required marketcap before coins are added to the big trusted exchanges (say random 40 million);

I'm curious for your insights.