This is somewhat of an anomaly book compared to the plethora of Battletech fiction. Of the earliest tomes, the story sets the stage for ramifications based around the Successor Houses and the intrigue thereof. However, the story does not heavily character develop, nor does it seek to explore multiple fronts of Successor House politics compared to later books. Really, it is a short story translated to novel length. The importance of the book is debatable as the events that follow pretty much explain the whys and wheres. However, for miscellaneous interest, the book has some worth, as one of the earliest forms of Battletech fiction if nothing else.
The caveat though is the book has a definite flavour that is NOT what Battletech ended up becoming under Stackpole, et al. influence. The book is somewhat less pervaded with the notion of "Good vs. Evil" that runs amok in Stackpole works and in that light, does its job. The character development is glacial, but is there, though as any first book, it tends to be more of an overview edition rather than a microscopic exploration. Certainly, the development though is likely to be disappointing compared to most other writers.
The notion of "western-esque" aspects could very well be correct. A close examination of the Warrior Trilogy, compared to this book, brings the objective examiner to the conclusion that Stackpole likely read far too much Flash Gordon and generally the Asian-influenced enemies of Stackpole books appear as laughable "Ming The Merciless" characters and continue a very objectionable stereotype. Stackpole is responsible for a great deal of the Succession War/Pre Clan era development despite the rumors of the story arc being laid out far in advance. He has said so himself. Yet, it should be noted, that the "East Evil - West Good" aspect was and is present even in this book to some degree, but holds none of the idiotic stereotyping pervading Stackpole's works. While every success of Battletech owes something to Stackpole, it also is reduced by continual "eon's time in a paragraph summary" habit which detracts more than enriches.
The Sword and the Dagger, in comparison, while dry, comes about as more a "flat plate" war story of a tad more grey game universe. The likely cause is few of the concepts of the modern Battletech universe were yet developed and aside from the technical characteristics, many of the initial universe characters were very one-dimensional. Indeed, a number of the characters in this book are not mentioned or seen again or even explored in later works. However, importantly, each side/faction involved in the "Sword and the Dagger" shows levels of resourcefulness and ability which is different from Stackpole's "one side wins all." Thus, further realism is acheived.
One thing this books excels at (as mentioned), more than any other of the following Battletech series, is the invasion sequence during the beginning of the story. The forces are balanced, surprise is backed logical reasoning, and the characters generally seem like real military personnel rather than the larger-than-life munchiness of the more recent books. When writing, that is a feature that is hard to acheive simply because the writer wishes that his characters have appeal - that one single quality alone means this book should rank higher than it does.
As to the relative worth, it is up the reader. I was not all too pleased to have spent five times the worth of the book only to find out that it did not overly appeal to me. So, it depends on the potential buyer and/or reader to come to his/her own conclusion as to whether the book is a sword or merely a dagger.