Dim Pro is a valuable part of the Sonar package. It has a lot of nice-sounding samples that in some cases surpass what's in the standard Kontakt factory library, e.g. Martin Acoustic Guitar. It's also pretty easy to use compared with Kontakt, and would suit beginners and intermediate-level enthusiasts just fine.
HOWEVER, as BitFlipper noted, a whole world of possibilities opens up for you when you have Kontakt. It's pretty much the industry-standard sampler. You can choose from not only NI's Komplete suite, but also tons of third-party libraries, many of which are free or very inexpensive. Example: the Indiginus Acoustic Guitar Collection ($40), which goes far beyond what you'll find in Dim Pro.
So, if you're serious about having the widest possible sonic palette, and the most powerful tools, you'll want to invest in Kontakt. It comes with lots of flexible editing, filtering, and mixing features, high-quality effects, and other goodies. Did I mention the included sample library? Lots of great stuff there -- I like the electric guitars, orchestral, and choral groups especially.
I don't think CW will ever try to update Dim Pro to match what Kontakt can do, nor do I think that would be a good use of resources. As it is, Dim Pro fits in with the Sonar suite very well.
Kontakt goes on sale pretty reguarly -- recently it could be had for $200. Until then, download the free Kontakt Player to get a feel for how it works. Have fun!
(Note: not affiliated with any of these companies, just a happy customer.)
Cheers,
Eddie