Is it worth patenting a software product?

The scope of your patent protection is determined by the claims. Patent attorneys try to draft claims that are difficult to design around, whether technologically or by making the design-arounds we anticipate economically less competitive. But the claims are typically amended and narrowed during the examination phase so at the time you make the patenting decision there's no way to know how broad your eventual patent coverage might be, or how hard it would be to design around your claims. Sorry, but that's just how the patenting process works.
BTW, if someone makes only a simple modification to yours, theirs is not patentable if that modification is an obvious one.