Were the United States's imperialistic ventures at the turn of the century (1898-1920) beneficial for the US or a misfortune for our nation?
I would argue that the only one of these "ventures" that was an unmitigated success for the US was the annexation of Hawaii. Other ventures, like the Spanish-American War, brought more misfortune than benefit.
The annexation of Hawaii was beneficial to the US because Hawaii became a state. Hawaii became an important part of the US economy and is now an integral part of the country. The only real down side to the annexation was its impact on the native Hawaiians.
Contrast that with our taking of the Philippines in the Spanish-American War. The main tangible impact of that for the US was that it helped pull us into WWII. In that case, the US tried to take a possession that was too far away to really be defended. By doing so, the US ended up having to spend lives and money to defend and then recapture a territory that was never really very useful to the US.
Depends on which angle you look at this issue, I suppose. Becoming a world power with colonies in both hemispheres, the US was able to project its military power and secure resources that have been vital to the growth of the American economy. It protected trade routes in Asia, and promoted security in the Caribbean. One could also argue that becoming an empire has hurt American democracy, denied human rights around the world, and made us dependent on foreign energy.
If you are focusing on the nation of the US, then certainly some ventures were beneficial, such as the acquisition of Hawaii. However, it is always important to look at such issues from both sides. Although Hawaii is now an accepted part of the United States, I don't imagine that they were particularly happy to be annexed at the time. The Spanish-American war, as pointed out above, was a mainly negative venture for the United States.