You certainly can buy a bluegrass machine when you want to, but the D 55 should work for you. Didn't Doc Watson play a D 55?
When talking about guitar types and bluegrass, why be a slave to convention? Our nephew-in-law is Rob McCoury, who is Del's son. He plays banjo in both the Del McCoury Band and also the Traveling McCourys. It doesn't get much more bluegrass than that and the last time we saw the Traveling McCourys here in Las Vegas, when we went backstage to say hi to Rob and do a meet and greet, the lead guitar player was playing (drumroll here....) a BREEDLOVE!! So there you go. Of course everything is amplified so you can make anything into a banjo killer.
Just throwing that out there for those who think you HAVE TO play a Martin. You don't.