The best reason to try APub is the one you stated: "I'd like to learn the program."

Only you can assess if it's better, has distinct advantages, for what you do as regards DTP.

For myself, it would because of, if for no other reason, APub's inclusion of master pages. As well as running headers, cross references, etc. My primary use of DTP is for books, but also posters, brochures, info-laden work, much of the proceeding coming from databases. XDP, as much as I love the product, is used more for static illustration that will be used in a layout application, though for certain posters and other one-page work, I'll often use XDP--nothing is faster to compose such things. I don't necessarily think of XDP versus XYZ as an either/or, but a both/and thing. Best tool for the job and all that.

That being said, there are better DTP applications, just more expensive.