If you add turbos or any other means of boosting sustained power output speeds will rise. After the deaths of Ratzenberger and Senna in 1994, the FIA has been doing everything possible to reduce the speeds which F1 cars reach. This has helped greatly to increase safety.
Should the FIA limit the engine size (less powerful engines), but allow turbos, I'm not sure what the point of this exercise would be? In one instant you are reducing power and then immediately afterwards, you are giving the engines extra power (turbos). Perhaps I am missing something here?
But then 10 years ago you wouldn't have expected a driver to have walked away from the accident that Webber had where he went upsidedown
Also top speed is limited by revs and gear ratios not power or boost
If you boost power output, on some tracks (like Monza or Hockenheim), there will be no question that the cars will be setup for optimum top speed. This will mean using long gear ratios, minimum wings, etc. The added engine power, will definitely lead to higher top speeds on the fastest parts of the track.
On a track like Hungary or Monaco, where high cornering speed is desirable: a more powerful engine will allow for higher cornering speed.
In both the above scenarios, by increasing power output, you are increasing speeds. When you increase speeds, you increase the likelihood of injury in the event of a crash.
Since 1994, safety has become a major factor when deciding the direction that F1 development should take.
The trend over the last few years seems to be that F1 cars have a top speed of around 200mph. Obviously, the FIA deem this to be acceptable. With this in mind, I can see engines getting smaller and perhaps becoming less powerful with time.