Okay, ICO's look more like the dot-com era ventures
On the other hand (just playing devil's advocate here), many dotcoms back then might have actually tried to make it but failed in the end, while what we see today seems to be more like deliberate scam attempts. Indeed, there should have been dotcoms that had never meant anything real right from the start, but the percentage should be significantly lower back in the day than it is nowadays. In a sense, people were more idealistic in late 1990's early 2000's, both investors and entrepreneurs alike. Investors weren't as greedy and cynical as they are today while entrepreneurs weren't as fishy and scammy
I wouldn't be so sure about the late 1990's being more idealistic and less greedy, but you pointed out an important factor: Deliberate scam attempts.
During the dot-com bubble the problem has huge overvaluations of companies with little to show for. With ICOs you have more of the same, with the added risk of scams attempts. Usually the latter would get filtered out early by regulations and a market of more experienced investors, but with ICOs you have neither in place. But maybe that's just my cynicism talking.
There is a big difference between the dot-com bubble and altcoins. Back then most financial magazines,papers and investment companies were pushing the investment potential of these stocks and funds. The result was millions of funds pouring in but the companies themselves did not make any profits. Now the knowledge base is between those who are aware of the products and understand the reasons behind the project. Gullible investors are not being targeted by commission hungry salesmen in financial adverts.
Gullible investors may not be targeted by hungry salesmen anymore, but they are still targeted with meaningless whitepapers, buzzwords and cookie-cutter fancy websites. I also doubt that the knowledge base has gotten much better since back then. Sure, people probably spend more time reading up on each project, but that's of little use without understanding the surrounding market, the underlying technologies and subsequently the challenges to be faced. The result is still the same: millions of funds poured into projects that do not make any profits.