Did the deaths of the powerful Dark Side users Darth Sidious and Darth Vader make the surviving Jedi more powerful? EDIT- Did the sudden void on the Dark Side affect the Force Sensitive on the Light Side?
Not in and of itself. The surviving Jedi were few, and only a few of those surviving Order 66 to this point would return to the Jedi path, many remained in obscurity. There is no evidence that the existence of Sith prevented the Jedi from tapping into their full potential - since the Force permeates all of the galaxy, it is not a zero-sum game.
However, the political situation was of course hostile towards Jedi, and force-users had to be wary while under Sidious' rule. Once they were defeated and killed, Jedi could once again begin to practice openly and seek out resources of Jedi wisdom. Palpatine kept a large amount of Sith and Jedi artifacts, and some of these would be recovered for use in Jedi training. Being able to train and learn from previously unavailable resources did enable the Jedi to rebuild their power. In addition, now that they could serve openly, new apprentices could be discovered and trained, thus adding to the Jedi's power.
So yes, their deaths did make the Jedi more powerful by removing a barrier to entry and learning.
Well I see the Force as both an energy field and an entity. Roan Shryne, a Jedi who survived Order 66 stated that he felt that some of the Force in the galaxy had run out as he was unable to loose a Force push to help an injured trooper. Sidious was clouding the Jedi's power. Once the Sith were dead, specifically Palpatine, you will notice that the feats of some NJO order Jedi to be higher than Old Republic Jedi. The Sith are gone. Sure you get a few pests like Keuller and Darth Caedus, but yes the Light Side was in an upswing, much better than when Plaugeis tipped the balance in Star Wars: Darth Plaugeis.