The short answer is NO. However, the information and knowledge you may be able to gain through your approach would be useful for further studies with respect to identification of new targets for therapy. Because your approach has certain limitations, complementary approaches will be needed to move forward.

Models of spheroid assays are much better than 2D cell culture assay to analyze the effect of anti-cancer drug. However, we need additional in vivo model to test the efficiency of any cancer drug.

As others have alluded, obviously there's no "the best" model, short of a phase 3 clinical trial.  

I think these kinds of models are interesting, as they allow you to ask certain questions that aren't accessible in 2D culture. For example, there has been some very interesting work in blood vessel formation in these types of hydrogel cultures.  You can image them, and measure their rate of growth.  So if you're a believer in the anti-angiogenesis approach, you might consider that.  (which I'm not, in the light of the well known absence of efficacy of certain overpriced blockbuster drugs, but that's a different story...).  But important and deep-pocketed people still do, so if your model is selling it to them, why not. 

In general, look for things that you can do with your model, that are difficult to do in other models.  I'm sure there are many legitimate uses. 

Thank you everybody for all your information and suggestions !