Diabetes in 7 year old dog - what's it doing to him

We have a 7 year old Yellow Lab who was diagnosed with diabetes about 1 year ago.  Since that time we have been giving him twice daily insulin doses and his blood sugars have been all over the place.  Earlier this year he lost most of his sight to cateracts but still tends to get around the house quite well.  We do not put him in unfamiliar surroundings any longer such as taking him to the pet store or to Grama and Grampa's house or anything like that due to the cateracts.  He tends to get a bit anxious -which is to be expected.  
His blood sugar has been all over the place at initial diagnosis it was 600something and more recently it has been at 367.  At the present time we are monitoring blood sugar at the vet on a weekly basis and his levels are still up.  We had considered doing a curve but the cost is too much at our vet.
My question is what is this uncontrolled diabetes doing to his insides?  his heart? kidneys? pancreas?  The doc says he has a strong heart but I'm wondering how she can really tell that.  We had asked if there was any blood test that we could do to determine if there was anything else wrong with him and they stated that if we did know that we wouldn't know the cause so it wasn't necessary to do that.
Also, i understand that a curve is important however doesn't that just show how his blood sugars fluctuate for that time frame?  Is there some sort of A1c test that can be done on canines similar to humans that can tell us more about his sugars over a longer period of time?

[ginger899]

Certainly a full senior blood panel can and should be done for him! That will help to know how his organs are working generally, and his white blood count, liver enzymes, etc etc. I can't see what the problem is about having this blood test done!

I'm sorry because I know very little about diabetes and its management.
But the blood panel is a good idea. If you are not satisfied with the way your vet is handling him, then please do go for a second opinion to another vet. Remember -we are paying them, therefore they are there to serve us and our pets.