Interesting question you pose.
Do you have permission from your boss to look at adwords account? If so then I would think that you should have access.. Agencies wont want you accessing account and making changes however as you mention its very useful to be able to see which keywords are gaining best ctr so that you can repeat in your SEO efforts. Forgive me for being cynical however their refusal to allow you access could hide a number of issues eg the change history will reveal how much work they are doing (or not). Even worse they could be spending your firms budget direct ads to other sites. If they wont allow you access you need to get some very good reasons indeed. Otherwise time for a new agency imho.