From the beginning, as we all know, Trek series have recycled guest actors in new roles. Partly, this is because it's hard to find people who can endure heavy alien prosthetics and still give a good performance, but I think "Enterprise" kicked it up a notch further. It seemed with virtually every episode we had at least one or two guest stars who'd played a role in a previous series. Certainly almost all the actors playing recurring characters (Forrest, Shran, Soval, Silik, Future Guy, Harris, and all the main Xindi) had played roles before. I suppose you could argue that it's fun to see if you can spot familiar actors (i.e. Suzie Plakson, Joseph Ruskin, Andreas Katsulas, John Schuck, Fionnula Flanagan) in new roles.
I noticed they even did something they hadn't really done before and cast series regulars
from previous series in new roles. I don't think most people considered "Oasis" or "Acquisition" very memorable, but I admit it was fun seeing Rene Auberjonois and Ethan Phillips in new roles, not to mention Roxann Dawson's voice coming out of that repair station computer in "Dead Stop". (Brent Spiner doesn't count).
I wonder if that would've continued, had the series gone on. I think it would've been neat to bring back, say Nana Visitor or Tim Russ (who done a number of different roles before Tuvok anyway).
Where there any regulars or guest stars from previous series you would've liked to see come back in a different role?