Interesting and without a doubt someof your points do hold water. But i'll take a whack at answering some of these
1. Do most foreigners who are native-Spanish speakers understand the average Dominican?
Some do, some don't. Many have a hard time with our various cadences, speech patterns and the plethora of words that come from either the Taino or African.
2. Does the average Dominican understands "standard" Spanish (Castilian)?
Of course. Sort of like Haitians who can readily understand French and Kreyol, while the French cannot understand Kreyol....
3. Have any of you taken into account that the Spanish spoken in the Caribbean has many influences from the Andalucian region and the Canary Islands dialect?
I have. What I have found in regards to Canary Islanders is that they were notorius for returning to their homelands. It is taken as fact by Canary Islanders themselves that their Spanish is influenced by Caribbean/ Venezuelen influences and not the other way around.
4. Have any of you taken into account that many of the Taino and African words that pepper Dominican Spanish are also found in the rest of the Spanish-speaking Caribbean?
This should come as know surprise since Taino dialects predominated the entire Caribbean. Even the Island Carib who were ethinically Cariban Speakers, spoke Arawakan dialects.Why? Because they raided the larger islands for women and in time their men and women spoke different languages.
5a. Have any of you taken into account that the Cibae?o dialect is not the only dialect (or maybe these are sub-dialect? :ermm

in the Dominican Republic?
Cibaeno dialect.......There are about four or five distinctive regional dialects on the island ( if one can call them dialects)
5b. If so, what would you say regarding the speech patterns in the eastern region? The south? La capital? Are these "new languages"? As far as I can tell, the few insisting in considering "Dominican Spanish" a separate language are only focusing on the Cibae?o dialect, almost completely ignoring the other dialects present in the country.
I for one am not insisting on making Dominican Spanish a distinctive Language. That can hardly be said, claimed or other wise. What can be said is that the regional forms of speech, along with the amount of words that can be attributed to African and especially Taino, makes our Spanish not just in the DR but PR and Cuba as well, very unique indeed.
5c. How can anyone say that Dominicans speak a local kreyol or patua o whatever, when the entire population doesn't speak in the same way? The differences are not only due to geography, but also economic status. There is a gulf between the Spanish spoken by the upper class vs. the lower class, and there is also another gulf between the regions.
The upper class and other elite portions of the population speak "better" due to education, etc. But the real Dominican is what is found in the Cibao, Maguana, Higuey, etc. Its amazing if not irresponisble the way many Dominicans make fun of the way campesinos speak when in fact this is who we are like it or not.
Compare the answers to other languages spoken in the region that are relatively new, like Haitian Kreyol, Papiamento (spelling?), English-patua, etc.
6. Are there enough similarities to effectively make the case that "Dominican Spanish" is in fact a new language, separate from "standard" Spanish?
Dominican Spanish...........which one? It can be surmised that we do indeed Speak Spanish. It can also be said that we have certain peculiarities in our own specific Spanish that makes it Uniquely ours. Just like Mexicans, Peruvians Etc. It may not be another language, but it sure as heck is ours and it is unique.
I wonder how many Castllian speakers feel about the way campesinos on out island speak and if they consider it........Spanish...like theirs.