Certainly don't be intimidated not to ask, work for the aforementioned Ryanair and we have had people up in the flightdeck during our turn-arounds. These mainly being parents with their children grabbing a look. As mentioned obviously pressures of quick turn-arounds generally mean it will only be brief visit unless you arrive early allowing a bit more time to take a look and ask questions and obviously no admittance to passengers in flight is allowed.
Regards