How much help can my U.S. Senator provide me with in regards to my claim rating?

Generally, a senator or congressperson will make an inquiry into your claim. This normally means a short letter asks the VA to either move your case along or look at a certain aspect of your claim. This can help a stalled claim be resolved, but it won't normally result in much else. After all, this person isn't going to take the time to peruse your claim file and make arguments on your behalf since they are not representing you in regards to your claim, but instead are ensuring that the VA operates efficiently in regards to the claim.

I'd suggest an incremental approach. Contact your Congress representative first. I did so when SallieMae was playing games with my school loans and it was fixed quite immediately.

Good question. Speaking from my own experience and that of fellow Veterans, I do not know that any influence can be put forth regarding the percentage of your rating, but getting an answer is a different issue. Representatives have assistants in their offices to help with public issues and fortunately for me, my Congressman had one that was well versed with VA issues. Within 72 hours of my phone call I had a photocopy of my claim with full rating and no more was that a problem. The really lousy thing, however, was that right before I called my Congressman, I had just talk to the VA benifits dept and got the same answer " it's still being processed". Here's the lousy part; the date on the approval for my claim and rating APPROVED was dated three weeks props to that phone call telling me that it was still being processed.
Having said all of this, I strongly advise you to consider this course of action carefully and do it in a timely manner and most of all, ensure that YOU do absolutely everything the VA requires. Do not miss any appointments. Turn in all documents they ask for, even if it's the forth time they ask for it. Keep a diary of who you talk to, when, where, topic, etc. Wait! This is a difficult one for some because for many reasons the delay in approval (or an answer) can cause one to think that their claim won't be approved. You MUST demonstrate that not only have you done all that has been required of you, you also waited a reasonable amount of time for the VA to do their job. Oh, and if you have not gone to one of the Service Organizations like the DAV, AL, VFW, put that at the top of your list. They have trained and certified Veteran Service Officers who are employed to help you do all of these important steps and can other support as well.
One last thing; when I retired there were groups of unscrupulous individuals often organized with a lawyer that would attempt to get you to sign on with them and for a percentage of the settlement they would help you settle your case. They would loophole it by having you apply for SSD or SSDI. Avoid them. They do not deserve a nickel of your money.
Good luck brother. Feel free to reach out to me if you like.