I say that every aspect of Darwin's notions of species is already contained in Genesis, and more comprehensively and scientifically posited.
Darwin was fighting the idea that Genesis posited a fixation of species. Darwin was suggesting that species were mutable, and that all animals from different kinds shared a common ancestor contrary to what Genesis claims.
Also, the definition of species has changed since Darwin's time. With the advent of the Modern Synthesis in the 1930's we now describe speciation with respect to genetic flow instead of Linnaean groupings.
I think what creationsts see re Darwins finches, are still finches with different beaks. More importantly they are still of the bird kind. 'Kinds' are broader than species. Creationists have common ancestors of sorts in that the wolf or wolf-like creature may well be the ancestor of all dog kinds today. Some creationists, including me, see a kind pegged at around the family rank level meaning common ancestors are there to a degree. It is just that the ancestors were created as their kind and variation is limited. Here is some evidence to back this up. The link below speaks to an organism ceasing to adapt while mutations continue to accrue.
The example of finches changing beak size, changes in colour in moths, changing alleles in bacteria is meant to be an observation that repeated many times will lead to a dinosaur evolving into a bird. This is the bit that creationists deny.
A bird changing beak size is an adaptation. These birds have adapted to their diet. It is a clever design that prevents two similar birds sucessfully breeding apart from geographic isolation. One reason may be the progeny may not be best suited to either environment.
There are evolutionary researchers that contest the bird to dino theory. Below is a link that speaks to it.
It is hard to change ones beliefs re creation given your researchers do not appear agreed on what other kind they are meant to have evolved from. It is hard to see species as any more than names given to in-kind variation, as opposed to support for common descent.
I also see that your cladistics get confusing and is in dispute around birds and lizards and mammals, with birds and mammals both being warm blooded, which of course Lizards are not. The link also has examples of the pluses and minuses for phylogenic and Linnaean classifications. The link below speaks to it.
I think that evolutionary evidence that any change or variation in a species, given a different name, is simply supplying a name for each in kind variation not dissimilar to naming humans different races. These are all human, just a little different from each other.
It will always be difficult to come up with a definition of species that is robust. If Neanderthal and human can mate and share 99.5% variability they meet all definitions of being human and have not speciated. Many even believe a chimp and human may reproduce viable offspring or sterile offspring. If this is the case then I guess one is also proposing speciation has not fully occured.
The same goes for other species that can sucessfully interbreed and belong to a different genus or family. They have not speciated sufficiently to produce a species barrier.
I think the definition of species is going to be problematic for some time to come. It is a concept that has no defining lines, obviously, so the blur from species to species, will always be vague, I expect.