Compared to what? I don't really understand your question here.
The BPX and BPVX and a matched surround speaker to the BP series speakers and they also can be used but don't exactly match perfectly with the Mythos series speakers.
Rear channel speakers are just as important as any speaker in ones home theater or multichannel music system. This is no "overpriced for rears" in my opinion.
If you feel rears are not important then buy some cheap speakers and use them for that duty. Why don't you take some time and learn about home theater and multichannel music. Once you get some knowledge under your hat, re read your question here.