I think Carolyn especially does know the best. From what I gather, these bells are of special interest to her. I agree fully that the unadorned brass ones are very nice too!
The bells that I see out there, that I believe Carolyn is talking about, are all the fancier ones unfortunately, I think I would only use them only as a high end benchmark for yours.
As for unadorned brass forms, the only one I found that was some what comparable to yours, was a wind up one sold back in September:
50s BOJ TURTLE Telephone/Hotel/Desk Bell/Ringer-NR-MIB (#390086669394), US $77.00,
Sorry but I don't know if the 'mechanical'(clockwork) forms are more or lesser value than the "manual" (no clockwork) form as I have not seen enough of them to tell. I suspect more, but I suggest that only from the point of view that the clockwork one would also have clockwork collectors interested in them (besides animal/turtle collectors and bell collector) and more competition usually means a higher price. However Scarcity would be another factor that could, for example, flip this around.
I think that the words I first heard from Carolyn sum it up well, (if I may paraphrase you Carolyn!): In the end, the bells are simply only worth what someone is willing to pay for them.
I do hope that Carolyn, Harry, and (to some small extent) I have been of some assistance! Carolyn and Harry are especially knowledgeable and a reliable source of great info!