A note on characterization. It's a fine line between homage and parody. No one can replace the cast that defined these characters for generations of viewers. I suppose it's a matter of channeling elements of the original performance in such a way so they seem to emerge naturally within a new actor's interpretation. Chris Doohan's take on Scotty is not exactly like his father's as it's filtered through Chris' own distinctive character. This is similar to Vic Mignogna's take on Kirk. Neither are or can be exactly like the originals, and even if they were it's questionable if the performances would feel natural.
Excellent point. I've actually been contemplating the same quandary as far as that fine line between parody and serious re-creation. And I think it really depends on the impetus and purpose the actor is looking for. I defer to the many Elvis impersonators or Beatles cover acts, and for that matter any impersonator of a well known actor. Many impersonators are also serious actors, and can play both sides of the range.
http://www.today.com/video/today/49694464#49694464