You can still let the old Bombadil voice in Bree and have the new one in the new instances. You already have a NPC like this: Radagast.
I love the old voice of Radagast in Lonelands (why do you disturb me?
) and I can understand that you made him to have a new voice in Vales of Anduin and such. It's understandable. And it's fine. The old voice is still there, and that's cool.
So why not make the same for Tom Bombadil? Let him say the good old hey dol merry dol my hearties in his house in the Old Forest, and have the new voice in the new instances.
Anamura, Sunnarea, Silenius, Neushiro, Wandrassa, Wuldar, Fingaladir, Meowear, Virgalia, Turgamar (Old Fegefeuer)
Amilegeth, Wargarr, Shakarabash, Luklubuz, Grishlukashkahkh, Dashkanakh
"One lag to lag them all and in the lagness lag them"