I've been pretty deep in this through board membership in several organizations.
As pointed out here, the T&C are important. Some contests are image harvesting for marketing purposes and claiming rights to use images in ongoing publications or marketing unrelated to the contest and without remuneration. In other cases, the T&C simply allow the organization to show submissions on their website and publicize the contest - which to me seems both reasonable and practical.
Fees serve several functions. Some organizations are setting fees and using contests to make a profit. Costs are relatively fixed, so the more entries the better. Well established contests with good prizes can be quite profitable. Fees can also be used to limit entries. I've seen people enter 10-20 images in a single contest even though there is a fee for entry. There are many different reasons - including supporting the organization. I like the idea of allowing lots of entries but using fees to impose a cost. Of course, fees also are used to cover the costs of the contest - software or tech support, judge honorariums, administration, marketing, and prizes.
Contest competition is very different. In a national or international contest, only exceptional images rise to the top. For example, with the NANPA Showcase, among the top 100 images more than 75% of wildlife photos involve action, with relatively few images that are portraits or environmental images. Landscape images need to be exception - with wonderful composition and lighting. With this in mind, making photos for competition means if lighting is not perfect, don't bother making images. Likewise for wildlife subject matter, it's all about great subjects in action. I like a point system for photos - much like PPA - where excellent photographs of ordinary subjects are recognized with points even if there are similar images. But in a large competition, it's only exceptional images that move to the top.
Another thing to consider with subject matter is the degree to which subjects are common or even cliches. Forget submitting iconic locations, large wading birds, or big mammals unless they are truly spectacular and unique. I judged a recent regional contest and there were 65 wading bird images, 11 osprey images - 9 of which had a fish, etc. In a national contest there are always many images of elk, deer, and black bears. Black bears don't catch fish. Brown bears catching fish are common, but often have good action. African mammals are popular but rarely unique. For landscapes, forget the common locations unless your image stands out compared to Ansel Adams or similar iconic photographs known by judges.