Should you build a dApp? It depends. What problem do you want to solve?
If you're just looking to learn how blockchain works, then sure, go for it. But if you're looking to build something that solves a real problem for real people, then it depends.
Blockchain is cool, but it's not a panacea. Consider your options before building a dApp. If the problem you want to solve exists in "the real world" then start with a real world solution. Talk to people. Write about it. Offer a service. Go knock on doors if you have to.
A dApp may very well help solve the problem, but don't start there. Go for the simplest solution, get feedback, and iterate. Put your customers first. Then maybe build a dApp.
Decentralization is a force for good, but so are you.
P.S. The world doesn't need another NFT collection. You can still build one to learn and make some money because there's demand, but look beyond the bottom line. Find a problem you care about that would actually benefit from decentralization.